Independent blade control system with hydraulic cyclic control

ABSTRACT

According to one embodiment, a radial fluid device includes a cylinder block having a plurality of radially extending cylinders, a plurality of pistons, and a cam disposed about the plurality of radially extending cylinders. A first linear control is coupled to the cam and operable to reposition the cam along a first axis. A second linear control is coupled to the cam and operable to reposition the cam along a second axis. A third linear control is coupled to the cam and operable to resist movement of the cam along a third axis.

TECHNICAL FIELD

This invention relates generally to rotorcraft blade control, and moreparticularly, to an independent blade control system with hydrauliccyclic control.

BACKGROUND

A rotorcraft may include one or more rotor systems. One example of arotorcraft rotor system is a main rotor system. A main rotor system maygenerate aerodynamic lift to support the weight of the rotorcraft inflight and thrust to counteract aerodynamic drag and move the rotorcraftin forward flight. Another example of a rotorcraft rotor system is atail rotor system. A tail rotor system may generate thrust in the samedirection as the main rotor system's rotation to counter the torqueeffect created by the main rotor system. A rotor system may include oneor more devices to rotate, deflect, and/or adjust rotor blades.

SUMMARY

Particular embodiments of the present disclosure may provide one or moretechnical advantages. A technical advantage of one embodiment mayinclude the capability to implement independent blade control on a rotorsystem. A technical advantage of one embodiment may include thecapability to provide a reliable independent blade control systemwithout the need for redundant electrical or mechanical systems,condition monitoring systems, or secondary load paths. A technicaladvantage of one embodiment may include the capability to control anindependent blade control system mechanically. A technical advantage ofone embodiment may include the capability to conserve power in anindependent blade control system.

Certain embodiments of the present disclosure may include some, all, ornone of the above advantages. One or more other technical advantages maybe readily apparent to those skilled in the art from the figures,descriptions, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

To provide a more complete understanding of the present invention andthe features and advantages thereof, reference is made to the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 shows a rotorcraft according to one example configuration;

FIG. 2 shows the rotor system and blades 120 of FIG. 1 according to oneexample configuration;

FIG. 3A shows the motion of the blades of FIG. 1 for a frequency of oneoscillation per revolution;

FIG. 3B shows the motion of the blades of FIG. 1 for a frequency ofthree oscillations per revolution;

FIG. 3C shows the motion of the blades of FIG. 1 for a frequency of fiveoscillations per revolution;

FIGS. 4A-4D shows the motions of the blades of FIG. 1 for a frequency offour oscillations per revolution;

FIG. 5A shows the motion of the blades of FIG. 1 for a frequency of twooscillations per revolution;

FIG. 5B shows the motion of the blades of FIG. 1 for a frequency of sixoscillations per revolution;

FIGS. 6A and 6B show an example hydraulic actuation system;

FIGS. 7A and 7B show another example hydraulic actuation;

FIGS. 8A and 8B show yet another example hydraulic actuation system;

FIGS. 8C and 8D show an example hydraulic actuation system having twocams;

FIG. 9A shows yet another example hydraulic actuation system accordingto one embodiment;

FIG. 9B shows the sum of each sinusoidal oscillation pattern generatedby the example hydraulic actuation system of FIG. 9A;

FIGS. 10A-10S show a radial fluid device and the frequencies of blademotions produced during operation of the radial fluid device accordingto one example embodiment;

FIGS. 11A-11K show an alternative embodiment of the radial fluid deviceof FIGS. 10A-10S and the frequencies of blade motions produced duringoperation of this alternative embodiment;

FIGS. 12A-12E show an individual blade control (IBC) system featuringthe radial fluid device of FIGS. 10A-10S according to one exampleembodiment;

FIGS. 13A-13K and 13M show a radial fluid device and the frequencies ofblade motions produced during operation of the radial fluid deviceaccording to another example embodiment;

FIG. 13L show an alternative embodiment of the radial fluid device ofFIGS. 13A-13K and 13M;

FIGS. 14A-14C show an IBC system featuring the radial fluid device ofFIGS. 13A-13J and 13M according to one example embodiment;

FIGS. 15A-15F show the blade actuators of the IBC system of FIGS.14A-14C according to one example embodiment;

FIG. 16A shows two of the blade actuators of FIGS. 15A-15F coupled inseries according to one example embodiment;

FIG. 16B shows three of the blade actuators of FIGS. 15A-15F coupled inseries according to one example embodiment;

FIG. 17A shows an IBC system featuring three of the radial fluid devicesof FIGS. 13A-13J and 13M and four sets of the coupled blade actuators ofFIG. 16B according to one example embodiment; and

FIG. 17B shows an IBC system featuring two of the radial fluid devicesof FIGS. 13A-13J and 13M and four sets of the coupled blade actuators ofFIG. 16A according to one example embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS Rotor Systems

FIG. 1 shows a rotorcraft 100 according to one example configuration.Rotorcraft 100 features a rotor system 110, blades 120, a fuselage 130,a landing gear 140, and an empennage 150. Rotor system 110 may rotateblades 120. Rotor system 110 may include a control system forselectively controlling the pitch of each blade 120 in order toselectively control direction, thrust, and lift of rotorcraft 100.Fuselage 130 represents the body of rotorcraft 100 and may be coupled torotor system 110 such that rotor system 110 and blades 120 may movefuselage 130 through the air. Landing gear 140 supports rotorcraft 100when rotorcraft 100 is landing and/or when rotorcraft 100 is at rest onthe ground. Empennage 150 represents the tail section of the aircraftand features components of a rotor system 110 and blades 120′. Blades120′ may provide thrust in the same direction as the rotation of blades120 so as to counter the torque effect created by rotor system 110 andblades 120. Teachings of certain embodiments relating to rotor systemsdescribed herein may apply to rotor system 110 and/or other rotorsystems, such as other tilt rotor and helicopter rotor systems. Itshould also be appreciated that teachings from rotorcraft 100 may applyto aircraft other than rotorcraft, such as airplanes and unmannedaircraft, to name a few examples.

FIG. 2 shows rotor system 110 and blades 120 of FIG. 1 according to oneexample configuration. In the example configuration of FIG. 2, rotorsystem 110 features a power train 112, a hub 114, a swashplate 116, andpitch links 118. In some examples, rotor system 110 may include more orfewer components. For example, FIG. 2 does not show components such as agearbox, a swash plate, drive links, drive levers, and other componentsthat may be incorporated.

Power train 112 features a power source 112 a and a drive shaft 112 b.Power source 112 a, drive shaft 112 b, and hub 114 are mechanicalcomponents for transmitting torque and/or rotation. Power train 112 mayinclude a variety of components, including an engine, a transmission,and differentials. In operation, drive shaft 112 b receives torque orrotational energy from power source 112 a and rotates hub 114. Rotationof rotor hub 114 causes blades 120 to rotate about drive shaft 112 b.

Swashplate 116 translates rotorcraft flight control input into motion ofblades 120. Because blades 120 are typically spinning when therotorcraft is in flight, swashplate 116 may transmit flight controlinput from the non-rotating fuselage to the hub 114, blades 120, and/orcomponents coupling hub 114 to blades 120 (e.g., grips and pitch horns).References in this description to coupling between a pitch link and ahub may also include, but are not limited to, coupling between a pitchlink and a blade or components coupling a hub to a blade.

In some examples, swashplate 116 may include a non-rotating swashplatering 116 a and a rotating swashplate ring 116 b. Non-rotating swashplatering 116 a does not rotate with drive shaft 112 b, whereas rotatingswashplate ring 116 b does rotate with drive shaft 112 b. In the exampleof FIG. 2, pitch links 118 connect rotating swashplate ring 116 b toblades 120.

In operation, according to one example embodiment, translating thenon-rotating swashplate ring 116 a along the axis of drive shaft 112 bcauses the pitch links 118 to move up or down. This changes the pitchangle of all blades 120 equally, increasing or decreasing the thrust ofthe rotor and causing the aircraft to ascend or descend. Tilting thenon-rotating swashplate ring 116 a causes the rotating swashplate 116 bto tilt, moving the pitch links 118 up and down cyclically as theyrotate with the drive shaft. This tilts the thrust vector of the rotor,causing rotorcraft 100 to translate horizontally following the directionthe swashplate is tilted.

Independent Blade Control

Independent blade control (IBC) may refer to the ability to controlmotion of individual rotor system blades, such as blades 120 a-120 d.For example, IBC may provide the ability to control harmonic motions ofindividual blades as the individual blades rotate. For discussionpurposes, harmonic blade motions may be separated into three categories:harmonic cyclic motions, harmonic collective motions, and reactionlessmotions. These three categories do not define any particularmechanization to drive the blades. Rather, these categories may bedefined by the characteristics of their oscillatory blade motions.

Harmonic cyclic motions may represent rotor blade sinusoidal motionssimilar to those that can be generated by application of oscillatoryswashplate tilting inputs to the non-rotating half of the swashplate. Inthe example of FIG. 2, harmonic cyclic motions may be similar to theapplication of tilting inputs to non-rotating swashplate ring 116 a.

The frequency of harmonic cyclic motions may be expressed as specificmultiple integers of rotor revolution frequency (e.g., revolutions perminute, or RPM). On a four-bladed rotor system such as rotor system 110,the frequencies of harmonic cyclic oscillations are odd integer values(e.g., one blade oscillation per revolution, 3/rev, 5/rev, 7/rev, etc.).

FIGS. 3A-3C show the motions of blades 120 a-120 d for frequencies ofone, three, and five blade oscillations per revolution. FIG. 3A showsthe motion of blades 120 a-120 d for a frequency of one oscillation perrevolution. One blade oscillation per revolution may be accomplished,for example, by maintaining non-rotating swashplate ring 116 a in afixed, tilted position. FIG. 3B shows the motion of blades 120 a-120 dfor a frequency of three oscillations per revolution. FIG. 3C shows themotion of blades 120 a-120 d for a frequency of five oscillations perrevolution.

Harmonic collective motions move all blades sinusoidally in phase witheach other. In the example of FIG. 2, harmonic collective motions may besimilar to the application of axial inputs to non-rotating swashplatering 116 a.

The frequency of harmonic collective motions may be expressed asspecific multiple integers of rotor revolution frequency (e.g., RPM). Inparticular, the frequency of harmonic collective motions may beexpressed as multiples of the number of blades on the rotor. On afour-bladed rotor system such as rotor system 110, the frequencies ofharmonic collective oscillations are 4/rev, 8/rev, etc. FIGS. 4A-4Dshows the motions of blades 120 a-120 d for a frequency of 4/rev. Asshown in FIGS. 4A-4D, blades 120 a-120 d move uniformly sinusoidally inphase with each other.

Unlike harmonic cyclic and collective motions, reactionless motionscannot be replicated by or analogized to swashplate motions. For afour-bladed rotor system, the frequencies of reactionless motions are2/rev and 6/rev, which cannot be achieved using the rotor system 110 ofFIG. 2. Oscillation frequencies of 2/rev and 6/rev for a four-bladedrotor system results in adjacent blades having a 180 degree phase lagand opposite blades being in phase with each other. FIG. 5A shows themotions of blades 120 a-120 d for a frequency of 2/rev, and FIG. 5Bshows the motions of blades 120 a-120 d for a frequency of 6/rev.Teachings of certain embodiments recognize that implementingreactionless controls may increase rotor system efficiency as well asreduce noise and vibration.

Thus, IBC may represent the ability to move rotor blades unconstrainedfrom the cyclic and collective kinematic motion limitations imposed byconventional swashplate controls. Although IBC is not a prerequisite toimplement cyclic and collective controls, it is a prerequisite toimplement reactionless controls.

Teachings of certain embodiments recognize the ability to implement IBCon a rotor system. For discussion purposes, IBC systems may be separatedinto two categories: partial authority and full authority.Partial-authority IBC systems sum their higher harmonic and reactionlesscontrol motions with a swashplate providing fundamental blade motion forcyclic and collective control. Full-authority IBC systems provide forindependent blade control through the full range of cyclic andcollective motion. In some circumstances, partial-authority IBC systemsmay be preferable because the total summed amplitudes of higher harmonicand reactionless motions are typically a relatively small percentage ofthe total blade travel required for cyclic and collective control.Therefore, the failure mode effects of partial-authority IBC actuatorsare not as critical as with full-authority systems, allowing for lesserlevels of reliability and redundancy. Full-authority IBC systems, on theother hand, may be preferable because they can allow for the eliminationof the swashplate and thus elimination of certain drag and weightpenalties.

Hydraulic Systems

Teachings of certain embodiments recognize the ability to implement IBCby hydraulically actuating the position of each rotor blade. FIGS. 6Aand 6B show an example hydraulic actuation system 200. Hydraulicactuation system 200 features a pump 210, control valves 220 (e.g.,electro-hydraulic valves), an actuator 230, and a reservoir 240. Inoperation, pump 210 provides hydraulic fluid to control valves 220,which either provides into or releases fluid out of actuator 230.Changing the volume of fluid in actuator 230 allows hydraulic actuationsystem 200 to either raise or lower load 250. Control valves 220 maypass hydraulic fluid to reservoir 240, which may provide hydraulic fluidto pump 210, as needed.

In the example of FIGS. 6A and 6B, hydraulic actuation system 200 is aconstant-pressure system in that pump 210 provides a constant pressureof hydraulic fluid. In a constant-pressure hydraulic system, the powerexpended to move the actuator is independent of the applied load on theactuator because power is a function of product flow and systempressure.

Maximum actuator rate capacity is achieved when control valves 220 arecommanded to their maximum orifice size, which is also the maximumoperating efficiency condition of hydraulic actuation system 200. Thus,the maximum operating efficiency condition occurs when load 250 islargest, as shown in FIG. 6A.

When less than maximum actuator rate is required (such as when load 250′is smaller, as shown in FIG. 6B), control valves 220 throttle down flowby reducing the orifice size and converting the unused power into wasteheat. Power is converted to even more waste heat when commanding controlvalves 220 to move actuator 230 at less than maximum rate in the samedirection as an aiding load. In addition to the power wasted throttlingdown the hydraulic flow going into actuator 230, hydraulic fluid beingpushed out the actuator 230 is also throttled by control valves 220squandering potentially regenerative power and converting it into heatwaste.

Adding a second set of actuators 230 for increased system reliabilitymay magnify this power waste more than a simple factor of two. Forredundancy, each control valve 220 would be independently capable ofproviding required power. This suggests that, when operating together,they both waste more than half the power they consume. Therefore thepower wasted by adding a second set of control valves 220 may increasethe power wasted and the heat generated by a factor of four.

By regulating the volume of fluid going in and out of a hydraulicactuator without throttling down flow, control valve power losses andthe resulting waste heat generation may be reduced or eliminated. FIGS.7A and 7B show an example hydraulic actuation system 300. Hydraulicactuation system 300 features a pump 310 and an actuator 320. Pump 310is a reversible-flow hydraulic pump featuring a swashplate 312 that maybe adjusted by control inputs 314. In operation, pump 310 may move aload 330 by changing the position of swashplate 312, which allows fluidto flow between the chambers of actuator 320. Thus, swashplate 312 mayprovide control over both displacement and flow direction.

Unlike hydraulic actuation system 200, hydraulic actuation system 300may provide control of actuator position without the throttling powerloss. However, application of this technology to IBC may be impracticaldue to performance, system complexity, weight, and control issues. Inparticular, the high relative inertia of swashplate 312 may not be ableto provide the frequency response required for IBC. In addition, afour-bladed rotor with dual redundancy would require a system of atleast eight pumps total because each actuator requires a dedicated pumpfor control.

Thus, although the power density and jam resistance of hydraulicactuation may make hydraulic actuation suitable for application to IBC,efficiency and inertia issues may make some hydraulic actuation systemsimpracticable. Teachings of certain embodiments, however, recognize thecapability to actuate loads in an IBC system without the wasted energyassociated with hydraulic actuation system 200 or the high inertiaproblems associated with hydraulic actuation system 300. In particular,teachings of certain embodiments recognize the capability to efficientlyand effectively actuate loads in an IBC system through the use ofmechanically-programmed cams.

FIGS. 8A and 8B show a hydraulic actuation system 400 according to oneexample embodiment. Hydraulic actuation system 400 features a cam 410and piston assemblies 420 and 430. Unlike hydraulic actuation system200, hydraulic actuation system 400 does not feature any control valvesto limit flow volume. Rather, piston assemblies 420 and 430 are porteddirectly to one another. Thus, hydraulic actuation system 400 may notsuffer from the energy losses associated with hydraulic actuation system200. In addition, unlike hydraulic actuation system 300, hydraulicactuation system 400 does not feature a swashplate and thus may not besubject to the inertia problems associated with hydraulic actuationsystem 300.

In operation, as shown in FIG. 8A, cam 410 pushes down the piston ofpiston assembly 420, which forces fluid into piston assembly 430, thusraising load 440. To lower load 440, as shown in FIG. 8B, cam 410 allowsthe piston of piston assembly 420 to pull up, which allows fluid to flowout of piston assembly 430, thus lowering load 440. Disregardingfriction losses, raising or lowering load 440 may be 100% efficientregardless of the size of load 440.

Teachings of certain embodiments recognize the ability to reduce thepower required to move a cam 410 by balancing loads between two cams410, as shown in FIGS. 8C and 8D. In this example, a cam shaft 450 joinstwo cams 410 together at 180 degrees out of phase. Disregarding leakageand friction losses, the sinusoidal raising and lowering of the cylinderloads would require no additional energy to sustain motion once aconstant speed of cam shaft 450 is achieved.

In addition, teachings of certain embodiments recognize the capabilityto program sinusoidal motion of a load by providing multiple cams ofdifferent shapes. As explained above with regard to the differentcategories of IBC motions, IBC motions may be expressed as specificintegers of rotor revolutions (e.g., for a four-blade rotor system, 1oscillation per revolution for cyclic motion, 2/rev for reactionlessmotion, 3/rev for cyclic motion, 4/rev for collective motion, 5/rev forcyclic motion, 6/rev for reactionless motion, etc.). Teachings ofcertain embodiments recognize the ability to program sinusoidal motionby providing a cam for each oscillation frequency and then hydraulicallysumming the outputs.

FIG. 9A shows a hydraulic actuation system 500 according to one exampleembodiment. Hydraulic actuation system 500 features a cam assembly 510,piston assemblies 520, and an actuator 530 operable to move a load 540.Each cam of cam assembly 510 is operable to oscillate a correspondingpiston of piston assemblies 520 according to the sinusoidal oscillationpatterns 560 shown in FIG. 9A.

In the example of FIG. 9A, cam assembly features six cams 511-516coupled to a cam shaft 550. Each cam 511-516 corresponds to a differentoscillation frequency. Cam 511, for example, is a single-lobed cam thatoscillates piston 521 once per revolution of cam shaft 550, as shown bysinusoidal oscillation pattern 561. Cam 512 is a two-lobed cam thatoscillates piston 522 twice per revolution of cam shaft 550, as shown bysinusoidal oscillation pattern 562. Cam 513 is a three-lobed cam thatoscillates piston 523 three times per revolution of cam shaft 550, asshown by sinusoidal oscillation pattern 563. Cam 514 is a four-lobed camthat oscillates piston 524 four times per revolution of cam shaft 550,as shown by sinusoidal oscillation pattern 564. Cam 515 is a five-lobedcam that oscillates piston 525 five times per revolution of cam shaft550, as shown by sinusoidal oscillation pattern 565. Cam 516 is asix-lobed cam that oscillates piston 526 six times per revolution of camshaft 550, as shown by sinusoidal oscillation pattern 566.

A precise waveform may be generated by hydraulically summing the outputsfrom each piston assembly 520. For example, FIG. 9B shows the sum ofeach sinusoidal oscillation pattern 560. As shown in FIG. 9B, the sum ofeach sinusoidal oscillation pattern 560 may result in a summedoscillation pattern 570 that is not sinusoidal.

With these concepts in mind, teachings of certain embodiments recognizethe capability to implement IBC on a rotor system, as discussed ingreater detail below.

Partial-Authority IBC

FIGS. 10A-10S show a radial fluid device 600 according to one exampleembodiment. Teachings of certain embodiments recognize that radial fluiddevice 600 may generate sinusoidal waveform amplitude andsynchronization displacement control to multiple actuators from a singleunit. As will be explained in greater detail below, the shape andsynchronization of these sinusoidal displacement changes may be definedby the corresponding volumetric sum of hydraulic fluid required todisplace each IBC actuator to replicate desired cyclic harmonic,collective harmonic, and reactionless blade motions. In this manner,radial fluid device 600 may emulate the hydraulic summation capabilitiesof hydraulic actuation system 500. In addition, teachings of certainembodiments recognize that radial fluid device 600 may emulate the powerconservation and regeneration capabilities of hydraulic actuation system400 by utilizing aiding actuator loads to drive radial fluid device 600as a hydraulic motor.

FIG. 10A shows a side view of radial fluid device 600, and FIG. 10Bshows a top view of radial fluid device 600. Radial fluid device 600features multiple stacked radial piston sections rotating together inconjunction with a common cylinder block 604 (not shown in FIGS. 10A and10B). In the example of FIGS. 10A-10S, radial fluid device 600 featuresstacked radial piston sections 620-660 and 620′-660′ rotating togetherwith shaft 602 and cylinder block 604.

As will be shown in greater detail below, shaft 602 is coupled tocylinder block 604. In some embodiments, shaft 602 is removably coupledto cylinder block 604. For example, different shafts 602 may havedifferent gear splines, and an installer may choose from among differentshafts 602 for use with radial fluid device 600.

Cylinder block 604 rotates within radial fluid device 600. In theexample of FIGS. 10A-10S, the axis of rotation of cylinder block 604 iscoaxial with shaft 602. Bearings may separate cylinder block 604 fromthe non-rotating body of radial fluid device 600.

Each pump section pair (e.g., sections 620 and 620′, 630 and 630′, etc.)is dedicated to generating the desired waveform for a specificfrequency. In the example of FIGS. 10A-10S, the pump section pairs arededicated to generating desired waveforms for 2/rev through 6/rev. Inthis example, the fundamental cyclic motions (1/rev) are generated by amechanical swashplate, such as swashplate 116 of FIG. 2.

Although the pump section pairs in radial fluid device 600 are dedicatedto generating desired waveforms for 2/rev through 6/rev, teachings ofcertain embodiments recognize that other fluid devices may include pumpsections dedicated to generating more, fewer, or different desiredwaveforms. For example, the performance benefits provided by somefrequencies may be minimal, and the pump sections generating thesefrequencies would be eliminated. As one example, a variation of radialfluid device 600 may only feature pump sections dedicated to 2/rev(reactionless) and 4/rev (collective harmonic), with the fundamentalcyclic motions (1/rev) generated by a mechanical swashplate.

Separate section frequencies from each pump section pair in radial fluiddevice 600 may be hydraulically summed together to generate a finaldesired waveform to each actuator, such as described above with regardto FIG. 9B. In particular, as will be explained in greater detail below,manifold 670 transmits the hydraulically summed fluids from radial fluiddevice 600 to actuators corresponding to each blade in a rotor system.

FIG. 10C shows a cross-section view of pump section 620 along thecross-section line indicated in FIG. 10B. In operation, pump section 620is operable to provide a hydraulic flow that results in reactionlessblade motions (2/rev) by blades 120 a-120 d, as shown in FIG. 10D. Inparticular, as shown in FIG. 10D, adjacent blades 120 a and 120 b are180 degrees out of phase, and opposite blades 120 a and 120 c are inphase. In this manner, the motion of blades in FIG. 10D resembles themotion of blades in FIG. 5A. As will be explained in greater detailbelow, teachings of certain embodiments recognize that using fourequally-spaced radial pistons driven by an elliptical cam may allow thevolume of fluid displaced by each piston to replicate the required 2/revreactionless sinusoidal motion and blade synchronization.

In the example of FIG. 10C, pump section 620 features four pistons 621a-621 d. Each piston 621 a-621 d is slidably received within acorresponding cylinder associated with chambers 604 a-604 d. As shown ingreater detail below, each chamber 604 a-604 d represents a plurality ofcylinders within cylinder block 604 that are in fluid communication.Each chamber 604 a-604 d may have an independent outlet port that exitsradial fluid device 600 to control a different IBC actuator.

Pump section 620 also features a cam 622. During operation, pistons 621a-621 d stroke inwards and outwards depending on the distance betweencam 622 and the axis of rotation of cylinder block 604. For example, cam622 is an elliptical cam having two lobes. As each piston 621 a-621 dmoves from the transverse diameter of cam 622 towards the conjugatediameter of cam 622, each piston 621 a-621 d will be pushed closer tothe axis of rotation of cylinder block 604. Likewise, as each piston 621a-621 d moves from the conjugate diameter of cam 622 to the transversediameter of cam 622, each piston 621 a-621 d will be pushed away fromthe axis of rotation of cylinder block 604. As a result, each piston 621a-621 d reciprocates towards and away from the axis of rotation ofcylinder block 604. Each reciprocation towards and away from the axis ofrotation thus includes two strokes: a down stroke and an up stroke.

In the example of FIG. 10C, cam 622 is elliptical and thus has twolobes. The number of lobes indicates how many sinusoidal stroke motionsa piston completes during one full rotation of cylinder block 604. Forexample, each piston 621 a-621 d completes two sinusoidal stroke motionsduring one rotation of cylinder block 604. The ability of pump section620 to complete two sinusoidal stroke motions during one rotationcorresponds to the two blade oscillations per revolution required forcertain reactionless blade motions.

Rotating cam 622 may change when pistons 621 a-621 d begin theirstrokes. For example, rotating cam 622 changes the location of thetransverse diameter of cam 622 and thus changes where each piston 621a-621 d begins a down stroke. As will be explained in greater detailbelow, moving cam 622 relative to the corresponding cam 622′ of pumpsection 620′ may change the amount of time between when correspondingpistons of pump sections 620 and 620′ begin their downstrokes. Teachingsof certain embodiments recognize that changing the amount of timebetween the downstrokes of corresponding pistons of pump sections 620and 620′ may change the maximum accessible cylinder volume of chambers604 a-604 d and therefore change how fluid flows in and out of radialfluid device 600.

Cam gear 623, drive gear 624, and cam adjuster 625 may, in combination,adjust the position of cam 622. Cam gear 623 is coupled to cams cam 622.Drive gear 624 interact with the teeth of cam gear 623. Cam adjuster 625rotates drive gear 624 such that drive gear 624 rotates cam gear 623. Asstated above, moving cams 622 changes when pistons 621 a-621 d begintheir strokes, and changing when pistons 621 a-621 d begin their strokescan change how fluid flows in and out of radial fluid device 600. Thus,teachings of certain embodiments recognize the ability to change howfluid flows in and out of radial fluid device 600 by changing theposition of cam adjuster 625.

In the example of FIG. 10C, cam gear 623 is a ring gear, drive gear 624is a worm gear, and cam adjuster 625 is an electric motor. Teachings ofcertain embodiments recognize that an electric-driven worm gear may beparticularly suitable for adjusting phase angle and amplitude for higherharmonics (e.g., 2/rev or greater) in an IBC system. In an IBC system,high-speed changes in phase angle and amplitude may not be required oreven desired for higher harmonics. For example, slow changes inelliptical cam phase angle may provide time for failure modes to beidentified and bypassed before undesirable blade motions are generated.In addition, a small-diameter worm gear running on a large-diameter ringgear may provide a high-gear reduction, thus reducing the torque of theelectric motor required and providing irreversibility in the event of amotor failure. In the event an electric motor should fail, theoscillatory motion may be nullified by the still operating pump section(e.g., pump section 620′) by indexing it's cam to an opposing phaseposition.

FIGS. 10E, 10F, and 10G show pump sections 620 and 620′ in operationwith their cams 622 and 622′ in phase. FIG. 10E shows a cross-sectionview of pump section 620 along the cross-section line indicated in FIG.10A, FIG. 10F shows a cross-section view of pump section 620′ along thecross-section line indicated in FIG. 10A, and FIG. 10G shows theresulting blade angle for blade 120 a that is produced by pump sections620 and 620′.

In operation, pump section 620, is operable to provide a hydraulic flowthat results in reactionless blade motions (2/rev) by blades 120 a-120d. As shown in FIG. 10F, pump section 620′ features pistons 621 a′-621d′, a cam 622′, a cam gear 623′, a drive gear 624′, and a cam adjuster625′. Each piston 621 a′-621 d′ is slidably received within acorresponding cylinder associated with chambers 604 a-604 d. In thismanner, corresponding pistons 621 a and 621 a′ share chamber 604 a,corresponding pistons 621 b and 621 b′ share chamber 604 b,corresponding pistons 621 c and 621 c′ share chamber 604 c, andcorresponding pistons 621 d and 621 d′ share chamber 604 d.

Cam 622′ is elliptical and thus has two lobes. Each piston 621 a′-621 d′completes two sinusoidal stroke motions during one rotation of cylinderblock 604. The ability of pump section 620′ to complete two sinusoidalstroke motions during one rotation corresponds to the two bladeoscillations per revolution required for certain reactionless blademotions.

Cam gear 623′, drive gear 624′, and cam adjuster 625′ may, incombination, adjust the position of cam 622′. In some embodiments, therelative positions of cams 622 and 622′ may be adjusted independently.For example, cams 622 and 622′ may be rotated in either the samedirection or opposite directions, and the distance of rotation of cam622 may not necessarily match the distance of rotation of 622′.

FIG. 10G shows the resulting blade angle for blade 120 a that isproduced by pump sections 620 and 620′ when cams 622 and 622′ are inphase. In this example, both pump sections 620 and 620′ are in phasesuch that pistons 621 a and 621 a′ complete their upstrokes and begintheir downstrokes at zero degrees and 180 degrees azimuth. In thisconfiguration, the sum of the sinusoidal waves generated by pumpsections 620 and 620′ is effectively double the contributing sinusoidalwaves.

FIGS. 10H, 10I, and 10J show pump sections 620 and 620′ in operationwhen their cams 622 and 622′ are 90 degrees out of phase. FIG. 10E showsa cross-section view of pump section 620 along the cross-section lineindicated in FIG. 10A, FIG. 10F shows a cross-section view of pumpsection 620′ along the cross-section line indicated in FIG. 10A, andFIG. 10G shows the resulting blade angle for blade 120 a that isproduced by pump sections 620 and 620′ when cams 622 and 622′ are 90degrees out of phase. As shown in FIG. 10H, cam 622 has been rotated 90degrees relative to its position shown in FIG. 10E.

In this example, both pump sections 620 and 620′ are 90 degrees out ofphase such that pistons 621 a and 621 a′ complete their upstrokes andbegin their downstrokes 90 degrees apart. In this configuration, thecontributing sinusoidal waves generated by pump sections 620 and 620′effectively cancel out. Thus, pump sections 620 and 620′ effectivelyhave no impact on flow in or out of chamber 604 a and therefore do notcause any reactionless motions by blade 120 a.

The examples of FIGS. 10G and 10J show how rotating cams 622 and 622′ inopposite directions relative to one another may change the effectiveflow volume of chamber 604 a and thus change the amplitude of the totalsinusoidal wave produced by the combination of pump sections 620 and620′. Teachings of certain embodiments recognize the ability to changethe phase of the total sinusoidal wave produced by the combination ofpump sections 620 and 620′ in addition to changing the amplitude. Inparticular, rotating cams 622 and 622′ in the same direction may changewhen the total sinusoidal wave reaches peak amplitude without changingthe magnitude of the peak amplitude.

In the example of FIGS. 10C-10J, pump sections 620 and 620′ includetwo-lobed (elliptical) cams capable of generating certain reactionlessblade motions. Teachings of certain embodiments recognize that radialfluid device 600 may also include additional pump sections capable ofgenerating different blade motions.

FIG. 10K shows a cross-section view of pump section 630 along thecross-section line indicated in FIG. 10B. In operation, pump section 630is operable to provide a hydraulic flow that results in cyclic blademotions (3/rev) by blades 120 a-120 d, as shown in FIG. 10L. In thismanner, the motion of blades in FIG. 10L resembles the motion of bladesin FIG. 3B.

Radial fluid device 600 also includes a corresponding pump section 630′.Pump sections 630 and 630′ may operate together to generate cyclic blademotions (3/rev) similarly to how pump sections 620 and 620′ operatetogether to generate reactionless blade motions (2/rev).

As shown in FIG. 10K, pump section 630 features pistons 631 a-631 d, acam 632, a cam gear 633, a drive gear 634, and a cam adjuster 635. Eachpiston 631 a-631 d is slidably received within a corresponding cylinderassociated with chambers 604 a-604 d. Similarly, each piston 631 a′-631d′ of pump section 630′ is also slidably received within a correspondingcylinder associated with chambers 604 a-604 d. In this manner,corresponding pistons 631 a and 631 a′ share chamber 604 a,corresponding pistons 631 b and 631 b′ share chamber 604 b,corresponding pistons 631 c and 631 c′ share chamber 604 c, andcorresponding pistons 631 d and 631 d′ share chamber 604 d. In addition,pistons 631 a and 631 a′, pistons 631 b and 631 b′, pistons 631 c and631 c′, and pistons 631 d and 631 d′ share chambers with pistons of theother pump sections of radial fluid device 600.

Cam 632 has three lobes. Each piston 631 a-631 d completes threesinusoidal stroke motions during one rotation of cylinder block 604. Theability of pump section 630 to complete three sinusoidal stroke motionsduring one rotation corresponds to the three blade oscillations perrevolution required for certain cyclic blade motions.

Cam gear 633, drive gear 634, and cam adjuster 635 may, in combination,adjust the position of cam 632. In some embodiments, the relativepositions of cams 632 and 632′ may be adjusted independently. Forexample, cams 632 and 632′ may be rotated in either the same directionor opposite directions, and the distance of rotation of cam 632 may notnecessarily match the distance of rotation of 632′.

FIG. 10M shows a cross-section view of pump section 640 along thecross-section line indicated in FIG. 10B. In operation, pump section 640is operable to provide a hydraulic flow that results in collective blademotions (4/rev) by blades 120 a-120 d, as shown in FIG. 10N. In thismanner, the motion of blades in FIG. 10N resembles the motion of bladesin FIGS. 4A-4D.

Radial fluid device 600 also includes a corresponding pump section 640′.Pump sections 640 and 640′ may operate together to generate collectiveblade motions (4/rev) similarly to how pump sections 620 and 620′operate together to generate reactionless blade motions (2/rev).

As shown in FIG. 10M, pump section 640 features pistons 641 a-641 d, acam 642, a cam gear 643, a drive gear 644, and a cam adjuster 645. Eachpiston 641 a-641 d is slidably received within a corresponding cylinderassociated with chambers 604 a-604 d. Similarly, each piston 641 a′-641d′ of pump section 640′ is also slidably received within a correspondingcylinder associated with chambers 604 a-604 d. In this manner,corresponding pistons 641 a and 641 a′ share chamber 604 a,corresponding pistons 641 b and 641 b′ share chamber 604 b,corresponding pistons 641 c and 641 c′ share chamber 604 c, andcorresponding pistons 641 d and 641 d′ share chamber 604 d. In addition,pistons 641 a and 641 a′, pistons 641 b and 641 b′, pistons 641 c and641 c′, and pistons 641 d and 641 d′ share chambers with pistons of theother pump sections of radial fluid device 600.

Cam 642 has four lobes. Each piston 641 a-641 d completes foursinusoidal stroke motions during one rotation of cylinder block 604. Theability of pump section 640 to complete four sinusoidal stroke motionsduring one rotation corresponds to the four blade oscillations perrevolution required for certain collective blade motions.

Cam gear 643, drive gear 644, and cam adjuster 645 may, in combination,adjust the position of cam 642. In some embodiments, the relativepositions of cams 642 and 642′ may be adjusted independently. Forexample, cams 642 and 642′ may be rotated in either the same directionor opposite directions, and the distance of rotation of cam 642 may notnecessarily match the distance of rotation of 642′.

FIG. 10O shows a cross-section view of pump section 650 along thecross-section line indicated in FIG. 10B. In operation, pump section 650is operable to provide a hydraulic flow that results in cyclic blademotions (5/rev) by blades 120 a-120 d, as shown in FIG. 10P. In thismanner, the motion of blades in FIG. 10P resembles the motion of bladesin FIG. 3C.

Radial fluid device 600 also includes a corresponding pump section 650′.Pump sections 650 and 650′ may operate together to generate cyclic blademotions (5/rev) similarly to how pump sections 620 and 620′ operatetogether to generate reactionless blade motions (2/rev).

As shown in FIG. 10M, pump section 650 features pistons 651 a-651 d, acam 652, a cam gear 653, a drive gear 654, and a cam adjuster 655. Eachpiston 651 a-651 d is slidably received within a corresponding cylinderassociated with chambers 604 a-604 d. Similarly, each piston 651 a′-651d′ of pump section 650′ is also slidably received within a correspondingcylinder associated with chambers 604 a-604 d. In this manner,corresponding pistons 651 a and 651 a′ share chamber 604 a,corresponding pistons 651 b and 651 b′ share chamber 604 b,corresponding pistons 651 c and 651 c′ share chamber 604 c, andcorresponding pistons 651 d and 651 d′ share chamber 604 d. In addition,pistons 651 a and 651 a′, pistons 651 b and 651 b′, pistons 651 c and651 c′, and pistons 651 d and 651 d′ share chambers with pistons of theother pump sections of radial fluid device 600.

Cam 652 has five lobes. Each piston 651 a-651 d completes fivesinusoidal stroke motions during one rotation of cylinder block 604. Theability of pump section 630 to complete five sinusoidal stroke motionsduring one rotation corresponds to the five blade oscillations perrevolution required for certain cyclic blade motions.

Cam gear 653, drive gear 654, and cam adjuster 655 may, in combination,adjust the position of cam 652. In some embodiments, the relativepositions of cams 652 and 652′ may be adjusted independently. Forexample, cams 652 and 652′ may be rotated in either the same directionor opposite directions, and the distance of rotation of cam 652 may notnecessarily match the distance of rotation of 652′.

FIG. 10Q shows a cross-section view of pump section 660 along thecross-section line indicated in FIG. 10B. In operation, pump section 660is operable to provide a hydraulic flow that results in reactionlessblade motions (6/rev) by blades 120 a-120 d, as shown in FIG. 10R. Inthis manner, the motion of blades in FIG. 10R resembles the motion ofblades in FIG. 5B.

Radial fluid device 600 also includes a corresponding pump section 660′.Pump sections 660 and 660′ may operate together to generate reactionlessblade motions (6/rev) similarly to how pump sections 620 and 620′operate together to generate reactionless blade motions (2/rev).

As shown in FIG. 10M, pump section 660 features pistons 661 a-661 d, acam 662, a cam gear 663, a drive gear 664, and a cam adjuster 665. Eachpiston 661 a-661 d is slidably received within a corresponding cylinderassociated with chambers 604 a-604 d. Similarly, each piston 661 a′-661d′ of pump section 660′ is also slidably received within a correspondingcylinder associated with chambers 604 a-604 d. In this manner,corresponding pistons 661 a and 661 a′ share chamber 604 a,corresponding pistons 661 b and 661 b′ share chamber 604 b,corresponding pistons 661 c and 661 c′ share chamber 604 c, andcorresponding pistons 661 d and 661 d′ share chamber 604 d. In addition,pistons 661 a and 661 a′, pistons 661 b and 661 b′, pistons 661 c and661 c′, and pistons 661 d and 661 d′ share chambers with pistons of theother pump sections of radial fluid device 600.

Cam 662 has six lobes. Each piston 661 a-661 d completes six sinusoidalstroke motions during one rotation of cylinder block 604. The ability ofpump section 660 to complete six sinusoidal stroke motions during onerotation corresponds to the six blade oscillations per revolutionrequired for certain reactionless blade motions.

Cam gear 663, drive gear 664, and cam adjuster 665 may, in combination,adjust the position of cam 662. In some embodiments, the relativepositions of cams 662 and 662′ may be adjusted independently. Forexample, cams 662 and 662′ may be rotated in either the same directionor opposite directions, and the distance of rotation of cam 662 may notnecessarily match the distance of rotation of 662′.

FIG. 10S shows a cross-section view of radial fluid device 600 along thecross-section line indicated in FIG. 10B. As shown in FIG. 10S, all pumpsections generating frequencies 2/rev through 6/rev are situated aboutthe same cylinder block 604. In addition, all pump sections share thesame chambers 604 a-604 d. Each chamber 604 a-604 d is ported out ofradial fluid device 600 through manifold 670. Manifold 670 may enablefluid communication between each chamber 604 a-604 d and a correspondingactuator with rotor blades 120 a-120 d (e.g., fluid communicationbetween chamber 604 a and the actuator associated with rotor blade 120a).

Teachings of certain embodiments recognize that radial fluid device 600may provide for IBC in a relatively compact space. For example, a 9000pound helicopter featuring a four-bladed rotor system operating at 3000PSI operating pressure may utilize a radial fluid device such as radialfluid device 600 that measures approximately 6 inches by 6 inches by 11inches (not including the cam adjusters). In this example, pump sections620 and 620′ may be sized to provide 20% of normal cyclic authoritywhile all other frequencies may be sized to provide 10% of normal cyclicauthority.

In some embodiments, cylinder block 604 may rotate at the same speed asdrive shaft 112 b. Teachings of certain embodiments recognize thatrotating cylinder block 604 at the same speed as drive shaft 112 b mayallow harmonic outputs from radial fluid device 600 to be synchronizedwith the rotor blades 120 a-120 d rotating about drive shaft 112 b. Inthe example of FIG. 10S, an exterior power source rotates shaft 602 atthe same speed as drive shaft 112 b, which causes cylinder block 604 toalso rotate at the same speed. Teachings of certain embodimentsrecognize that radial fluid device 600 may be well suited to operate atthe same speed as drive shaft 112 b. For example, helicopter hydraulicpumps in other settings may operate at approximately 5000 RPM andindustrial radial pumps of similar displacements as radial fluid device600 may operate at approximately 1500 RPM, whereas as rotor speeds aretypically lower than these speeds (e.g., 400 to 500 RPM).

In the example of FIGS. 10A-10S, radial fluid device 600 is configuredto provide IBC in a four blade rotor system. Teachings of certainembodiments recognize, however, recognize that the concepts describedwith regard to radial fluid device 600 may be adapted to support IBC forrotor systems with more or fewer blades (e.g., two blades, three blades,five blades, six blades, seven blades, etc.) by adapting the arrangementof pistons, cams, and porting. For example, FIGS. 11A-11K shows a radialfluid device 700 configured to provide IBC in a five blade rotor system.

FIG. 11A shows a top view of radial fluid device 700. Radial fluiddevice 700 features multiple stacked radial piston sections rotatingtogether in conjunction with a common cylinder block 6704 (not shown inFIG. 10A). In the example of FIGS. 11A-11J, radial fluid device 700features stacked radial piston sections 720-760 and 720′-760′ rotatingtogether with shaft 702 and cylinder block 704.

As will be shown in greater detail below, shaft 702 is coupled tocylinder block 704. In some embodiments, shaft 702 is removably coupledto cylinder block 704. For example, different shafts 702 may havedifferent gear splines, and an installer may choose from among differentshafts 702 for use with radial fluid device 600.

Cylinder block 704 rotates within radial fluid device 700. In theexample of FIGS. 11A-11J, the axis of rotation of cylinder block 704 iscoaxial with shaft 702. Bearings may separate cylinder block 704 fromthe non-rotating body of radial fluid device 700.

Each pump section pair (e.g., sections 720 and 720′, 730 and 730′, etc.)is dedicated to generating the desired waveform for a specificfrequency. In the example of FIGS. 11A-11J, the pump section pairs arededicated to generating desired waveforms for 2/rev through 6/rev. Inthis example, the fundamental cyclic motions (1/rev) are generated by amechanical swashplate, such as swashplate 116 of FIG. 2.

Although the pump section pairs in radial fluid device 700 are dedicatedto generating desired waveforms for 2/rev through 6/rev, teachings ofcertain embodiments recognize that other fluid devices may include pumpsections dedicated to generating more, fewer, or different desiredwaveforms. For example, the performance benefits provided by somefrequencies may be minimal, and the pump sections generating thesefrequencies would be eliminated. As one example, a variation of radialfluid device 700 may only feature pump sections dedicated to 2/rev(reactionless) and 4/rev (collective harmonic), with the fundamentalcyclic motions (1/rev) generated by a mechanical swashplate.

Separate section frequencies from each pump section pair in radial fluiddevice 700 may be hydraulically summed together to generate a finaldesired waveform to each actuator, such as described above with regardto FIG. 9B. In particular, as will be explained in greater detail below,manifold 770 transmits the hydraulically summed fluids from radial fluiddevice 700 to actuators corresponding to each blade in a rotor system.

In this example embodiments, pump sections 730-760 and 730′-760′ ofradial fluid device 700 may operate in a similar manner to pump sections630-660 and 630′-660′ of radial fluid device 600. For example, FIG. 11Bshows a cross-section view of pump section 730 along the cross-sectionline indicated in FIG. 11A. In operation, pump section 730 is operableto provide a hydraulic flow that results in cyclic blade motions (3/rev)by blades 120 a-120 d, as shown in FIG. 11C. In this manner, the motionof blades in FIG. 11C resembles the motion of blades in FIG. 3B.

Radial fluid device 700 also includes a corresponding pump section 730′.Pump sections 730 and 730′ may operate together to generate cyclic blademotions (3/rev) similarly to how pump sections 730 and 730′ operatetogether to generate cyclic blade motions (3/rev).

As shown in FIG. 11B, pump section 730 features pistons 731 a-731 e, acam 732, a cam gear 733, a drive gear 734, and a cam adjuster 735. Eachpiston 731 a-731 e is slidably received within a corresponding cylinderassociated with chambers 704 a-704 e. Similarly, each piston 731 a′-731e′ of pump section 730′ is also slidably received within a correspondingcylinder associated with chambers 704 a-704 e. In this manner,corresponding pistons 731 a and 731 a′ share chamber 704 a,corresponding pistons 731 b and 731 b′ share chamber 704 b,corresponding pistons 731 c and 731 c′ share chamber 704 c,corresponding pistons 731 d and 731 d′ share chamber 704 d, andcorresponding pistons 731 e and 731 e′ share chamber 704 e. In addition,pistons 731 a and 731 a′, pistons 731 b and 731 b′, pistons 731 c and731 c′, pistons 731 dc and 731 d′, and pistons 731 e and 731 e′ sharechambers with pistons of the other pump sections of radial fluid device700.

Cam gear 733, drive gear 734, and cam adjuster 735 may, in combination,adjust the position of cam 732. In some embodiments, the relativepositions of cams 732 and 732′ may be adjusted independently. Forexample, cams 732 and 732′ may be rotated in either the same directionor opposite directions, and the distance of rotation of cam 732 may notnecessarily match the distance of rotation of 732′.

FIG. 11D shows a cross-section view of pump section 740 along thecross-section line indicated in FIG. 11A. In operation, pump section 740is operable to provide a hydraulic flow that results in collective blademotions (4/rev) by blades 120 a-120 d, as shown in FIG. 11E. In thismanner, the motion of blades in FIG. 11E resembles the motion of bladesin FIGS. 4A-4D.

Radial fluid device 700 also includes a corresponding pump section 740′.Pump sections 740 and 740′ may operate together to generate collectiveblade motions (4/rev) similarly to how pump sections 640 and 640′operate together to generate collective blade motions (4/rev).

As shown in FIG. 11D, pump section 740 features pistons 741 a-741 e, acam 742, a cam gear 743, a drive gear 744, and a cam adjuster 745. Eachpiston 741 a-741 e is slidably received within a corresponding cylinderassociated with chambers 704 a-704 e. Similarly, each piston 741 a′-741e′ of pump section 740′ is also slidably received within a correspondingcylinder associated with chambers 704 a-704 e. In this manner,corresponding pistons 741 a and 741 a′ share chamber 704 a,corresponding pistons 741 b and 741 b′ share chamber 704 b,corresponding pistons 741 c and 741 c′ share chamber 704 c,corresponding pistons 741 d and 741 d′ share chamber 704 d, andcorresponding pistons 741 e and 741 e′ share chamber 704 e. In addition,pistons 741 a and 741 a′, pistons 741 b and 741 b′, pistons 741 c and741 c′, pistons 741 d and 741 d′, and pistons 741 e and 741 e′ sharechambers with pistons of the other pump sections of radial fluid device700.

Cam gear 743, drive gear 744, and cam adjuster 745 may, in combination,adjust the position of cam 742. In some embodiments, the relativepositions of cams 742 and 742′ may be adjusted independently. Forexample, cams 742 and 742′ may be rotated in either the same directionor opposite directions, and the distance of rotation of cam 742 may notnecessarily match the distance of rotation of 742′.

FIG. 11F shows a cross-section view of pump section 750 along thecross-section line indicated in FIG. 11A. In operation, pump section 750is operable to provide a hydraulic flow that results in cyclic blademotions (5/rev) by blades 120 a-120 d, as shown in FIG. 11G. In thismanner, the motion of blades in FIG. 11G resembles the motion of bladesin FIG. 3C.

Radial fluid device 700 also includes a corresponding pump section 750′.Pump sections 750 and 750′ may operate together to generate cyclic blademotions (5/rev) similarly to how pump sections 650 and 650′ operatetogether to generate cyclic blade motions (5/rev).

As shown in FIG. 11F, pump section 750 features pistons 751 a-751 e, acam 752, a cam gear 753, a drive gear 754, and a cam adjuster 755. Eachpiston 751 a-751 e is slidably received within a corresponding cylinderassociated with chambers 704 a-704 e. Similarly, each piston 751 a′-751e′ of pump section 750′ is also slidably received within a correspondingcylinder associated with chambers 704 a-704 e. In this manner,corresponding pistons 751 a and 751 a′ share chamber 704 a,corresponding pistons 751 b and 751 b′ share chamber 704 b,corresponding pistons 751 c and 751 c′ share chamber 704 c,corresponding pistons 751 d and 751 d′ share chamber 704 d, andcorresponding pistons 751 e and 751 e′ share chamber 704 e. In addition,pistons 751 a and 751 a′, pistons 751 b and 751 b′, pistons 751 c and751 c′, pistons 751 d and 751 d′, and pistons 751 e and 751 e′ sharechambers with pistons of the other pump sections of radial fluid device700.

Cam gear 753, drive gear 754, and cam adjuster 755 may, in combination,adjust the position of cam 752. In some embodiments, the relativepositions of cams 752 and 752′ may be adjusted independently. Forexample, cams 752 and 752′ may be rotated in either the same directionor opposite directions, and the distance of rotation of cam 752 may notnecessarily match the distance of rotation of 752′.

FIG. 11H shows a cross-section view of pump section 760 along thecross-section line indicated in FIG. 11A. In operation, pump section 760is operable to provide a hydraulic flow that results in reactionlessblade motions (6/rev) by blades 120 a-120 d, as shown in FIG. 11I. Inthis manner, the motion of blades in FIG. 11I resembles the motion ofblades in FIG. 5B.

Radial fluid device 700 also includes a corresponding pump section 760′.Pump sections 760 and 760′ may operate together to generate reactionlessblade motions (6/rev) similarly to how pump sections 660 and 660′operate together to generate reactionless blade motions (6/rev).

As shown in FIG. 11H, pump section 760 features pistons 761 a-761 e, acam 762, a cam gear 763, a drive gear 764, and a cam adjuster 765. Eachpiston 761 a-761 e is slidably received within a corresponding cylinderassociated with chambers 704 a-704 e. Similarly, each piston 761 a′-761e′ of pump section 760′ is also slidably received within a correspondingcylinder associated with chambers 704 a-704 e. In this manner,corresponding pistons 761 a and 761 a′ share chamber 704 a,corresponding pistons 761 b and 761 b′ share chamber 704 b,corresponding pistons 761 c and 761 c′ share chamber 704 c,corresponding pistons 761 d and 761 d′ share chamber 704 d, andcorresponding pistons 761 e and 761 e′ share chamber 704 e. In addition,pistons 761 a and 761 a′, pistons 761 b and 761 b′, pistons 761 c and761 c′, pistons 761 d and 761 d′, and pistons 761 e and 761 e′ sharechambers with pistons of the other pump sections of radial fluid device700.

Cam gear 763, drive gear 764, and cam adjuster 765 may, in combination,adjust the position of cam 762. In some embodiments, the relativepositions of cams 762 and 762′ may be adjusted independently. Forexample, cams 762 and 762′ may be rotated in either the same directionor opposite directions, and the distance of rotation of cam 762 may notnecessarily match the distance of rotation of 762′.

In the examples of FIGS. 11B-11I, each piston is ported sequentially toa corresponding blade actuator with the 72 degree radial spacing for thefive-blade frequencies of 3/rev, 4/rev, 5/rev, and 6/rev. For 2/revreactionless motion using an elliptical cam, however, teachings ofcertain embodiments recognize that piston ports may be crossed in pumpsection 720 for a five-bladed rotor system. In particular, cross-portingmay allow fluid device 700 to use pistons with 72 degree spacing togenerate blade motions of 144 degree spacing, which may satisfyrequirements of 2/rev reactionless motions.

FIG. 11J shows a cross-section view of pump section 720 along thecross-section line indicated in FIG. 11A. In operation, pump section 720is operable to provide a hydraulic flow that results in reactionlessblade motions (2/rev) by blades 120 a-120 d, as shown in FIG. 11K. Inthis manner, the motion of blades in FIG. 11K resembles the motion ofblades in FIG. 5A.

Radial fluid device 700 also includes a corresponding pump section 720′.Pump sections 720 and 720′ may operate together to generate reactionlessblade motions (2/rev) similarly to how pump sections 620 and 620′operate together to generate reactionless blade motions (2/rev), exceptthat the piston ports in pump section 720 are crossed for a five-bladedrotor system.

As shown in FIG. 11J, pump section 720 features pistons 721 a-721 e, acam 722, a cam gear 723, a drive gear 724, and a cam adjuster 725. Eachpiston 721 a-721 e is slidably received within a cylinder associatedwith chambers 704 a-704 e. However, unlike pump sections 730-760, thecorrespondence between pistons 721 a-721 e and chambers 704 a-704 e iscrossed for some pistons. In the example of FIG. 11J, piston 721 a isslidably received within a cylinder associated with chamber 704 a,piston 721 b is slidably received within a cylinder associated withchamber 704 c, piston 721 c is slidably received within a cylinderassociated with chamber 704 e, piston 721 d is slidably received withina cylinder associated with chamber 704 b, and piston 721 e is slidablyreceived within a cylinder associated with chamber 704 d. Similarly,piston 721 a′ is slidably received within a cylinder associated withchamber 704 a, piston 721 b′ is slidably received within a cylinderassociated with chamber 704 c, piston 721 c′ is slidably received withina cylinder associated with chamber 704 e, piston 721 d′ is slidablyreceived within a cylinder associated with chamber 704 b, and piston 721e′ is slidably received within a cylinder associated with chamber 704 d.In this manner, corresponding pistons 721 a and 721 a′ share chamber 704a, corresponding pistons 721 b and 721 b′ share chamber 704 c,corresponding pistons 721 c and 721 c′ share chamber 704 e,corresponding pistons 721 d and 721 d′ share chamber 704 b, andcorresponding pistons 721 e and 721 e′ share chamber 704 d. In addition,pistons 721 a and 721 a′, pistons 721 b and 721 b′, pistons 721 c and721 c′, pistons 721 d and 721 d′, and pistons 721 e and 721 e′ sharechambers with pistons of the other pump sections of radial fluid device700.

Cam gear 723, drive gear 724, and cam adjuster 725 may, in combination,adjust the position of cam 722. In some embodiments, the relativepositions of cams 722 and 722′ may be adjusted independently. Forexample, cams 722 and 722′ may be rotated in either the same directionor opposite directions, and the distance of rotation of cam 722 may notnecessarily match the distance of rotation of 722′.

Implementing Partial-Authority IBC

As stated above, radial fluid device 600 may provide sinusoidal waveformamplitude and synchronization displacement control to multiple actuatorsfor use in a partial-authority IBC system. For example, radial fluiddevice 600 may include pump section pairs dedicated to generatingdesired waveforms for 2/rev through 6/rev. In this example, thefundamental cyclic motions (1/rev) are generated by a mechanicalswashplate, such as swashplate 116 of FIG. 2. As will be explained ingreater detail below, teachings of certain embodiments recognize thecapability to convert harmonic pressure changes in hydraulic fluidwithin radial fluid device 600 into movements of blades 120 a-120 d.

FIG. 12A shows an IBC system 800 according to one example embodiment.IBC system 800 is a partial-authority IBC system that features radialfluid device 600, a hydraulic control manifold 810, a hydraulic swivel820, four pitch link actuators 830 a-830 d (corresponding to rotorblades 120 a-120 d), a hydraulic pump 840, a hydraulic reservoir 850,and a heat exchanger 860.

As shown in FIGS. 12A-12E, IBC system 800 may include a variety of fluidlines that provide fluid communication between multiple components. Forconvenience, some of these fluid lines have been labeled “a,” “b,” “c,”“d,” “e,” or “f.” In these example embodiments, labels “a”-“d”correspond with chambers 604 a-604 d and blades 120 a-120 d. Forexample, fluid line “a” may represent a fluid line in the path betweenchamber 604 a and blade 120 a. Fluid line “e” may refer to system fluid,and fluid line “f” may refer to return fluid, both of which aredescribed in greater detail below.

In operation, according to one example embodiment, radial fluid device600 provides hydraulic fluid to hydraulic control manifold 810.Hydraulic control manifold directs the fluid through hydraulic swivel820, which is configured to transfer the fluid flow from the fixed-frameportion of the rotorcraft to the rotating-frame portion of therotorcraft. In one example embodiment, hydraulic swivel 820 provides thefluid up along the drive shaft to pitch link actuators 830 a-830 d,which converts pressure changes in the supplied hydraulic fluid intomovements of rotor blades 120 a-120 d.

In addition to providing fluid from radial fluid device 600 to pitchlink actuators 830 a-830 d, IBC system 800 also provides system fluidfrom hydraulic pump 840 to pitch link actuators 830 a-830 d. This systemfluid represents a constant-pressure fluid supply. Teachings of certainembodiments recognize that the supply fluid may not necessarily stayconstant, such as due to leakage or other effects that may change thepressure of the supply fluid. The supply fluid may be provided to pitchlink actuators 830 a-830 d to provide a balance against the pressures ofthe hydraulic fluid from radial fluid device 600. Excess fluid may alsobe accumulated through hydraulic control manifold 810 and hydraulicswivel 820, passed through heat exchanger 860, and stored in hydraulicreservoir 850 before being resupplied to hydraulic pump 840.

FIG. 12B shows hydraulic control manifold 810 according to one exampleembodiment. Hydraulic control manifold 810 features valves 812 andcontrol ports 814.

In operation, according to one example embodiment, hydraulic controlmanifold 810 receives fluid from chambers 604 a-604 d of radial fluiddevice 600 and communicates the fluid to valves 812 and control ports814. In this example embodiment, hydraulic control manifold 810 receivesthe fluid from chambers 604 a-604 d through manifold 670, which rotateswith cylinder block 604. Manifold 670 includes ports for each chamber604 a-604 d. In addition, manifold 670 includes seals around each portfor chambers 604 a-604 d. Furthermore, manifold 670 includes returnports to accumulate leaking hydraulic fluid and return the accumulatedhydraulic fluid to reservoir 850.

Radial fluid device 600 may not include provisions for independentlytrimming pitch link actuator stroke position to equalize their lengthsand maintain IBC operation about a center stroke. Accordingly, hydrauliccontrol manifold 810 may include valves 812 operable to trim theposition of each pitch link actuator 830 a-830 d and to compensate forleaking hydraulic fluid. In one example embodiment, valves 812 arethree-way direct drive valves.

Valves 812 may add supply fluid to fluid lines a-d if the fluid pressurefalls below a threshold. Alternatively, valves 812 may remove fluid fromfluid lines a-d associated if the fluid pressure rises about athreshold. In one example embodiment, valves 812 receives measurementsfrom position sensors associated with pitch link actuators 830 a-830 dand then adds fluid to or removes fluid from the fluid lines a-d basedon the received measurements. The measurements from the position sensorsmay indicate, for example, the amount of fluid that has leaked fromvarious fluid lines within IBC system 800. As another example, themeasurements from the position sensors may indicate whether fluid linepressure should be adjusted to trim the position of each pitch linkactuators 830 a-830 d.

In one example embodiment, valves 812 may adjust for drift and leakagein IBC system 800, but valves 812 may not drive high-frequency changesin system pressure. Rather, high-frequency changes may be implemented byradial fluid device 600. Teachings of certain embodiments recognize thatonly using valves for low-frequency changes in system pressure mayreduce the necessary size of the valves and increase longevity of thevalves.

Control ports 814 communicate fluid between hydraulic control manifold810 and hydraulic swivel 820. Teachings of certain embodiments recognizethat control ports 814 may also terminate fluid flow in the event ofsome system failures. In the example of FIG. 12B, each control port 814is equipped with a solenoid bypass valve. In the event of apartial-authority system failure requiring isolation from theconventional flight control system, for example, IBC system 800 mayremove power to the solenoid bypass valves associated with each controlport 814. In response, control ports 814 cut off pressure to theirpressure relief/bypass valves, causing them to redirect system fluid tothe hydraulic fluid return lines f that lead back to reservoir 850.Redirecting system fluid prevents the system fluid from reaching thepitch link actuators 830 a-830 d, which as will be explained in greaterdetail below, causes the pitch link actuators 830 a-830 d to lock attheir center stroke position.

FIG. 12C shows hydraulic swivel 820 according to one example embodiment.Hydraulic swivel 820 includes a rotating portion 822 and a stationaryportion 824. Rotating portion 822 includes ports 822 a-822 d thatcommunicates fluid between pitch link actuators 830 a-830 d andnon-rotating portion 824. Rotating portion 822 also includes port 822 e,which communicates system fluid between pitch link actuators 830 a-830 dand non-rotating portion 824. Rotating portion 822 includes port 822 f,which communicates return fluid between pitch link actuators 830 a-830 dand non-rotating portion 824.

Rotating portion also includes rotary seals 823 between each port 822a-822 f. Teachings of certain embodiments recognize that providing bothport 822 f for return fluid and seals 823 may extend seal life andreduce or eliminate issues associated with nuisance leakage.

Rotating portion also includes wiring for communicating signals frompitch link actuators 830 a-830 d to the non-rotating portions of IBCsystem 800. In one example embodiment, the wiring includes wires foreach position sensor associated with the pitch link actuators 830 a-830d plus three common wires providing excitation power.

Stationary portion 824 includes fluid lines 824 a-824 d thatcommunicates fluid between ports 822 a-822 d and fluid lines a-d.Stationary portion 824 also includes fluid line 824 e, whichcommunicates fluid between port 822 e and fluid line e. Stationaryportion 824 includes fluid line 824 f, which communicates fluid betweenport 822 f and fluid line f.

FIG. 12D shows pitch link actuator 830 a according to one exampleembodiment. Pitch link actuator 830 a is operable to change the positionof blade 120 a during operation of rotorcraft 100. Similarly, pitch linkactuators 830 b-830 d are operable change the positions of blades 120b-120 d, respectively.

In one example embodiment, pitch link actuator 830 a may be coupledbetween hub 114 and swashplate 116 such that pitch link actuator 830 amay change the distance between hub 114 and swashplate 116. In thisexample, pitch link actuator 830 a is coupled between hub 114 andswashplate 116 but not necessarily coupled to hub 114 and/or swashplate116. For example, pitch link actuator 830 a may be coupled to othercomponents in mechanical communication with hub 114 and/or swashplate116. In addition, pitch link actuator 830 a may only change onemeasurement of a distance between hub 114 and swashplate 116. Forexample, pitch link actuator 830 a may change the distance between hub114 and swashplate 116 proximate to pitch link actuator 830 a, whereasthe distance between hub 114 and swashplate 116 proximate to pitch linkactuator 830 b may remain the same.

In the example of FIG. 12D, pitch link actuator 830 a includes a linearhydraulic actuator that includes a piston 832 a that separates a controlchamber 831 a from a system chamber 833 a. Control chamber 831 areceives fluid from line a. System chamber 833 a receives controlledsystem fluid from line e. In operation, piston 832 a moves in responseto a pressure difference between fluid in control chamber 831 a andfluid in system chamber 833 a.

In the example of FIG. 12D, piston 832 a is unbalanced. The piston areaon the side of control chamber 831 a is greater than the piston area onthe side of system chamber 833 a. In this example, system fluid insystem chamber 833 a may prevent hydraulic cavitation from occurring bycreating a constant-force, hydraulic-spring effect on piston 832 a.

Teachings of certain embodiments recognize that pitch link actuators 830a-830 d may conserve hydraulic power during operation. For example,during higher-harmonic cyclic and reactionless motions, the total netflow used by pitch link actuators 830 a-830 d may be near zero due tothe summed opposing sinusoidal flow demands canceling. For example,during reactionless motions, a downstroke by piston 832 a may be offsetby an upstroke by piston 832 b.

On the other hand, higher-harmonic collective motions may requiresignificantly more fluid to move all blades sinusoidally in unison. Inthis example, pitch link actuators 830 a-830 d may push a large volumeof fluid back into the remaining components of IBC system 800 or pull alarge volume of fluid out of the remaining components of IBC system 800.Teachings of certain embodiments recognize, however, that hydraulicaccumulator may capture and recover this hydraulic energy on therotor-frame side of IBC system 800. In the example of FIG. 12A, thehydraulic accumulator is connected to the system fluid line e.

In the example of FIG. 12D, pitch link actuator 830 a also includes aposition sensor 834 a. Position sensor 834 a may measure thedisplacement distance of piston 832 a. One example of position sensor834 a may include a linear variable differential transformer. Positionsensor 834 a may be used as part of a feedback control system. Forexample, the cams of radial fluid device 600 may be programmed so as toproduce an expected displacement distance of piston 832 a. If positionsensor 834 a measures a displacement distance different from theexpected displacement distance, one or more problems could be the cause.For example, IBC system 800 could be leaking fluid, which may change thepressure difference between fluid in chambers 831 a and 833 a, whichwould change the displacement distance of piston 832 a. In response, IBCsystem 800 may take one or more corrective actions. As one example, thecams of radial fluid device 600 may be repositioned to achieve theexpected displacement distance. As another example, valves 812 may addfluid to or remove fluid from the fluid lines (e.g., fluid lines a-e) toadjust the fluid pressures in pitch link actuator 830 a. In someembodiments, adjusting the cams of radial fluid device 600 may be moreappropriate for making large changes in fluid pressure, whereasadjusting valves 812 may be more appropriate for smaller changes ortrimming of fluid pressure.

In the example of FIG. 12D, pitch link actuator 830 a also includes astroke lock 836 a. Stroke lock 836 a may prevent piston 832 a frommoving in the event of system failure. As shown in FIG. 12D, stroke lock836 a separates the system fluid from a spring. The spring provides anopposing force to the pressure from the system fluid. If, for example,the pressure from the system fluid is reduced or eliminated, force fromthe spring pushes the spring lock 836 a towards piston 832 a andprevents piston 832 a from moving, as shown in FIG. 12E. Such a scenariomight occur, for example, if control port 814 e prevents system fluidfrom reaching pitch link actuator 830 a.

Full-Authority IBC

The example radial fluid device 600, described above, generatesdisplacement changes to drive higher-harmonic motions (e.g., 2/revthrough 6/rev) but does not necessarily generate fundamental cyclicmotions (e.g., 1/rev). In some embodiments, it may be possible forradial fluid device 600 to provide fundamental cyclic motions byproviding a single-lobed pump section similar to pump section 620. Insome circumstances, however, fundamental cyclic motions must beimplemented more quickly than higher-harmonic motions because the pilotmay steer the direction of the rotorcraft through fundamental cyclicmotions. In these circumstances, the radial piston approach used byradial fluid device 600 to implement higher-harmonic motions may be tooslow for fundamental cyclic motions. Thus, in some embodiments, thehigher-harmonic approach described with regard to radial fluid device600 may not be suitable for fundamental cyclic motions.

In some embodiments, it may also be possible to implement fundamentalcyclic motions using the valves 812 of IBC system 800. For example,valves 812 may be capable of changing fluid line pressures so as toimplement fundamental cyclic motions on pitch link actuators 830 a-830d. As explained above, however, valves 812 may be more suitable forimplementing small pressure changes, whereas fundamental cyclic motionsmay require large pressure changes in the fluid lines. Increasing thevalve flow gain in valves 812 to implement these large pressure changesmay increase the risk of hard-over failures. In addition, the powerconsumed and heat generated by valves 812 in this scenario may raiseadditional issues.

Teachings of certain embodiments recognize the capability to generatefundamental cyclic actuator motions quickly while still protectingagainst hard-over failures, conserving hydraulic power, and minimizingheat generation. Teachings of certain embodiments also recognize thecapability to eliminate the mechanical rotor swashplate from a rotorsystem by hydraulically generating the fundamental cyclic motions.

FIGS. 13A-M show a radial fluid device 900 according to one exampleembodiment. FIG. 13A shows a side view of radial fluid device 900, andFIG. 13B shows a top view of radial fluid device 900. Radial fluiddevice 900 features multiple stacked radial piston sections rotatingtogether in conjunction with a common cylinder block 904 (not shown inFIGS. 13A and 13B).

In the example of FIGS. 13A-13M, radial fluid device 900 features afundamental cyclic pump 910 as well as stacked radial piston sections920-960 and 920′-960′ rotating together with shaft 902, cylinder block904, and manifold 970. Embodiments of stacked radial piston sections920-960 and 920′-960′ may resemble and operate similarly to stackedradial piston sections 620-660 and 620′-660′.

As will be shown in greater detail below, shaft 902 is coupled tocylinder block 904. In some embodiments, shaft 902 is removably coupledto cylinder block 904. For example, different shafts 902 may havedifferent gear splines, and an installer may choose from among differentshafts 902 for use with radial fluid device 600.

Cylinder block 904 rotates within radial fluid device 900. In theexample of FIGS. 10A-10M, the axis of rotation of cylinder block 904 iscoaxial with shaft 902. Bearings may separate cylinder block 904 fromthe non-rotating body of radial fluid device 900.

Fundamental cyclic pump 910 and each pump section pair (e.g., sections920 and 920′, 930 and 930′, etc.) are dedicated to generating thedesired waveform for a specific frequency. In the example of FIGS.13A-13M, fundamental cyclic pump 910 is dedicated to generating desiredwaveforms for fundamental cyclic motions (1/rev), and the pump sectionpairs are dedicated to generating desired waveforms for 2/rev through6/rev.

Although the pump section pairs in radial fluid device 900 are dedicatedto generating desired waveforms for 2/rev through 6/rev, teachings ofcertain embodiments recognize that other fluid devices may include pumpsections dedicated to generating more, fewer, or different desiredwaveforms. For example, the performance benefits provided by somefrequencies may be minimal, and the pump sections generating thesefrequencies would be eliminated. As one example, a variation of radialfluid device 900 may only feature pump sections dedicated to 2/rev(reactionless) and 4/rev (collective harmonic), with the fundamentalcyclic motions (1/rev) generated by fundamental cyclic pump 910.

Separate section frequencies from fundamental cyclic pump 910 and eachpump section pair in radial fluid device 900 may be hydraulically summedtogether to generate a final desired waveform to each actuator, such asdescribed above with regard to FIG. 9B. In particular, as will beexplained in greater detail below, manifold 970 transmits thehydraulically summed fluids from radial fluid device 900 to actuatorscorresponding to each blade in a rotor system.

FIG. 13C shows a cross-section view of fundamental cyclic pump 910 alongthe cross-section line indicated in FIG. 13B. Fundamental cyclic pump910 features four pistons 911 a-911 d. Each piston 911 a-911 d isslidably received within a corresponding cylinder associated withchambers 904 a-904 d. Each chamber 904 a-904 d represents a plurality ofcylinders within cylinder block 904 that are in fluid communication.Each chamber 904 a-904 d may have an independent outlet port that exitsradial fluid device 900 to control a different IBC actuator.

Fundamental cyclic pump 910 also features cam 912. During operation,pistons 911 a-911 d stroke inwards and outwards depending on thedistance between cam 912 and the axis of rotation of cylinder block 904.Each piston 911 a-911 d reciprocates towards and away from the axis ofrotation of cylinder block 604. Each reciprocation towards and away fromthe axis of rotation thus includes two strokes: a down stroke and an upstroke.

In the example of FIG. 13C, cam 912 is a circular cam and has one lobe.The number of lobes indicates how many sinusoidal stroke motions apiston completes during one full rotation of cylinder block 904. Forexample, each piston 911 a-911 d completes one sinusoidal stroke motionduring one rotation of cylinder block 904. The ability of fundamentalcyclic pump 910 to complete one sinusoidal stroke motion during onerotation corresponds to the one blade oscillation per revolutionrequired for fundamental cyclic motions.

Repositioning cam 912 may change the displacement distance for eachpiston 911 a-911 d. In the example of FIG. 13C, positioning pistons 913,914, and 915 may reposition cam 912. In this example, positioning piston913 is coupled to cam 912, and positioning pistons 914 and 915 arecoupled to a crank associated with cam 912.

Cam 912 may be repositioned by varying the pressure in at least one ofthe cylinders associated with positioning pistons 913, 914, and 915.Positioning pistons 913, 914, and 915 may allow cam 912 to be translatedin two perpendicular axis, similar to swashplate lateral andlongitudinal motions. The housing surrounding cam 912 may be dimensionedto provide stops limiting lateral and longitudinal cyclic travel.

In the example of FIG. 13C, fluid in the cylinder associated withpositioning piston 913 is maintained at a relatively constant systempressure, and fluid in the cylinders associated with positioning pistons914 and 915 may be varied to reposition cam 912. Positioning piston 913may operate as a hydraulic spring to oppose the forces exerted bypositioning pistons 914 and 915.

In the example of FIG. 13C, fundamental cyclic pump 910 includesposition sensors 916 and 917. Position sensors 916 and 917 may measurethe displacement distance of positioning pistons 914 and 915,respectively. One example of position sensor may include a linearvariable differential transformer.

Valves 918 and 919 may provide fluid to the cylinders associated withpositioning pistons 913, 914, and/or 915. In some embodiments, valves918 and 919 may change the size of their orifices to vary the pressureof fluid in the cylinders associated with positioning pistons 914 and95. In one example embodiment, valves 918 and 919 are three-way directdrive valves. In some embodiments, valves 918 and 919 may be single coilor dual coil three-way valves.

In some circumstances, if cylinder block 904 is rotating (such as atrotor speed) and cam 912 is positioned concentric with the input shaftaxis, pistons 911 a-911 d do not stroke. This scenario results in nofluid displacement control changes being sent to the IBC actuators forfundamental cyclic motions.

Translating cam 912 away from this concentric position, however, mayresult in fluid displacement control changes being sent to the IBCactuators for fundamental cyclic motions. FIG. 13D, for example, showshow retracting positioning pistons 914 and 915 may reposition cam 912.The example of FIG. 13D may correspond to a full-forward longitudinalcyclic position in some scenarios. Moving cam 912 as shown in FIG. 13Dresults in fundamental cyclic motions by each blade 120 a-120 d, asshown in FIG. 13E.

As another example, FIG. 13F shows how extending positioning pistons 914and 915 may reposition cam 912. The example of FIG. 13F may correspondto a full-aft cyclic position in some scenarios. Moving cam 912 as shownin FIG. 13F results in fundamental cyclic motions by each blade 120a-120 d, as shown in FIG. 13G. Comparing the examples of FIGS. 13E and13G, blade 120 a in FIG. 13E is 180 degrees out of phase with blade 120a in FIG. 13G.

Fundamental cyclic pump 910 may also implement lateral cyclic motions aswell as longitudinal cyclic motions. FIG. 13H, for example, shows howretracting positioning piston 914 and extending 915 may reposition cam912. The example of FIG. 13H may correspond to a full-left lateralcyclic position in some scenarios. Moving cam 912 as shown in FIG. 13Hresults in fundamental cyclic motions by each blade 120 a-120 d, asshown in FIG. 13I.

As another example, FIG. 13J shows how extending positioning piston 914and retracting positioning piston 915 may reposition cam 912. Theexample of FIG. 13J may correspond to a full-right longitudinal positionin some scenarios. Moving cam 912 as shown in FIG. 13J results infundamental cyclic motions by each blade 120 a-120 d, as shown in FIG.13K. Comparing the examples of FIGS. 13I and 13K, blade 120 a in FIG.13I is 180 degrees out of phase with blade 120 a in FIG. 13K. Comparingthe examples of FIGS. 13E and 13I, blade 120 a in FIG. 13E is 90 degreesout of phase with blade 120 a in FIG. 13I.

In the example of FIGS. 13A-13K, fundamental cyclic pump 910 isconfigured to provide fundamental cyclic motions in a four blade rotorsystem. Teachings of certain embodiments recognize, however, recognizethat the concepts described with regard to fundamental cyclic pump 910may be adapted to support IBC for rotor systems with more or fewerblades (e.g., two blades, three blades, five blades, six blades, sevenblades, etc.).

For example, FIG. 13L shows a fundamental cyclic pump 910′ configured toprovide IBC in a five-blade rotor system. In this example, fundamentalcyclic pump 910′ features five pistons 911 a′-911 e′ corresponding toeach blade in the five-blade rotor system. Fundamental cyclic pump 910′also features a cam 912′, positioning pistons 913′-915′, positionsensors 916′ and 917′, and valves 918′ and 919′ that may operate in asimilar manner to corresponding components in fundamental cyclic pump910.

FIG. 13M shows a cross-section view of radial fluid device 900 along thecross-section line indicated in FIG. 13B. As shown in FIG. 13M,fundamental cyclic pump 910 and all pump sections generating frequencies2/rev through 6/rev are situated about the same cylinder block 904. Inaddition, fundamental cyclic pump 910 and all pump sections share thesame chambers 904 a-904 d. Each chamber 904 a-904 d is ported out ofradial fluid device 900 through manifold 970. Manifold 970 may enablefluid communication between each chamber 904 a-904 d and a correspondingactuator with rotor blades 120 a-120 d (e.g., fluid communicationbetween chamber 904 a and the actuator associated with rotor blade 120a).

In some embodiments, cylinder block 904 may rotate at the same speed asdrive shaft 112 b. Teachings of certain embodiments recognize thatrotating cylinder block 904 at the same speed as drive shaft 112 b mayallow harmonic outputs from radial fluid device 900 to be synchronizedwith the rotor blades 120 a-120 d rotating about drive shaft 112 b. Inthe example of FIG. 13M, an exterior power source rotates shaft 902 atthe same speed as drive shaft 112 b, which causes cylinder block 904 toalso rotate at the same speed.

Implementing Full-Authority IBC

As stated above, radial fluid device 900 may provide sinusoidal waveformamplitude and synchronization displacement control to multiple actuatorsfor use in a full-authority IBC system. For example, radial fluid device900 may include a fundamental cyclic pump and pump section pairsdedicated to generating desired waveforms for 1/rev through 6/rev. Inthis example, the mechanical swashplate, such as swashplate 116 of FIG.2, may be eliminated of the rotor system. As will be explained ingreater detail below, teachings of certain embodiments recognize thecapability to convert harmonic pressure changes in hydraulic fluidwithin radial fluid device 900 into movements of blades 120 a-120 d.

FIG. 14A shows an IBC system 1000 according to one example embodiment.IBC system 1000 is a full-authority IBC system that features radialfluid device 900, a hydraulic control manifold 1100, a hydraulic swivel1200, four blade actuators 1300 a-1300 d (corresponding to rotor blades120 a-120 d), a hydraulic pump 1400, a hydraulic reservoir 1500, and aheat exchanger 1600.

As shown in FIGS. 14A-14C and 15A-15E, IBC system 1000 may include avariety of fluid lines that provide fluid communication between multiplecomponents. For convenience, some of these fluid lines have been labeled“a,” “b,” “c,” “d,” “e,” or “f.” In these example embodiments, labels“a”-“d” correspond with chambers 904 a-904 d and blades 120 a-120 d. Forexample, fluid line “a” may represent a fluid line in the path betweenchamber 904 a and blade 120 a. Fluid line “e” may refer to system fluid,and fluid line “f” may refer to return fluid, both of which aredescribed in greater detail below.

In operation, according to one example embodiment, radial fluid device900 provides hydraulic fluid to hydraulic control manifold 1100.Hydraulic control manifold directs the fluid through hydraulic swivel1200, which is configured to transfer the fluid flow from thefixed-frame portion of the rotorcraft to the rotating-frame portion ofthe rotorcraft. In one example embodiment, hydraulic swivel 1200provides the fluid up along the drive shaft to blade actuators 1300a-1300 d, which converts pressure changes in the supplied hydraulicfluid into movements of rotor blades 120 a-120 d.

In addition to providing fluid from radial fluid device 900 to bladeactuators 1300 a-1300 d, IBC system 1000 also provides system fluid fromhydraulic pump 1400 to blade actuators 1300 a-1300 d. This system fluidrepresents a constant-pressure fluid supply. Teachings of certainembodiments recognize that the supply fluid may not necessarily stayconstant, such as due to leakage or other effects that may change thepressure of the supply fluid. The supply fluid may be provided to bladeactuators 1300 a-1300 d to provide a balance against the pressures ofthe hydraulic fluid from radial fluid device 900. Excess fluid may alsobe accumulated through hydraulic control manifold 1100 and hydraulicswivel 1200, passed through heat exchanger 1600, and stored in hydraulicreservoir 1500 before being resupplied to hydraulic pump 1400.

FIG. 14B shows hydraulic control manifold 1100 according to one exampleembodiment. Hydraulic control manifold 1100 features valves 1112 andcontrol ports 1114.

In operation, according to one example embodiment, hydraulic controlmanifold 1100 receives fluid from chambers 904 a-904 d of radial fluiddevice 900 and communicates the fluid to valves 1112 and control ports1114. In this example embodiment, hydraulic control manifold 1100receives the fluid from chambers 904 a-904 d through manifold 970, whichrotates with cylinder block 904. Manifold 970 includes ports for eachchamber 904 a-904 d. In addition, manifold 970 includes seals aroundeach port for chambers 904 a-904 d. Furthermore, manifold 970 includesreturn ports to accumulate leaking hydraulic fluid and return theaccumulated hydraulic fluid to reservoir 1500.

Radial fluid device 900 may not include provisions for independentlytrimming blade actuator stroke position to equalize their lengths andmaintain IBC operation about a center stroke. Accordingly, hydrauliccontrol manifold 1100 may include valves 1112 operable to trim theposition of each blade actuator 1300 a-1300 d and to compensate forleaking hydraulic fluid. In one example embodiment, valves 1112 arethree-way direct drive valves.

Valves 1112 may add supply fluid to fluid lines a-d if the fluidpressure falls below a threshold. Alternatively, valves 1112 may removefluid from fluid lines a-d if the fluid pressure rises about athreshold. In one example embodiment, valves 1112 receives measurementsfrom position sensors associated with blade actuators 1300 a-1300 d andthen adds fluid to or removes fluid from fluid lines a-d based on thereceived measurements. The measurements from the position sensors mayindicate, for example, the amount of fluid that has leaked from variousfluid lines within IBC system 1000. As another example, the measurementsfrom the position sensors may indicate whether fluid line pressureshould be adjusted to trim the position of each blade actuators 1300a-1300 d.

In one example embodiment, valves 1112 may adjust for drift and leakagein IBC system 1000, but valves 1112 may not drive high-frequency changesin system pressure. Rather, high-frequency changes may be implemented byradial fluid device 900. Teachings of certain embodiments recognize thatonly using valves for low-frequency changes in system pressure mayreduce the necessary size of the valves and increase longevity of thevalves.

Unlike partial-authority IBC system 800, full-authority IBC system 1000includes two valves 1112 for each rotor blade (e.g., two valves 1112 afor rotor blade 120 a). Teachings of certain embodiments recognize thatmultiple valves 1112 may be capable of providing fundamental collectiveinput. In some embodiments, additional valves 1112 may add or removefluid from the volume trapped between radial fluid device 900 and bladeactuators 1300. Because the high-frequency flow providing fundamentalcyclic and IBC is controlled by radial fluid device 900, valves 900 maybe relatively low gain, thus minimizing the impact of a valve hard-overfailure.

Even with a relatively low gain, a valve hard-over failure on afull-authority IBC actuator could create rotor instability if notbypassed quickly. Teachings of certain embodiments recognize thatredundant systems may be appropriate for full-authority IBC systemsbecause of the risks associated with removing the mechanical swashplatefrom the rotor system. Accordingly, the example full-authority IBCsystem 1000 includes redundant valves 1112 for each rotor blade. Byincorporating two valves per IBC actuator, hard-over failures may bequickly bypassed by commanding the second valve in the oppositedirection.

Control ports 1114 communicate fluid between hydraulic control manifold1100 and hydraulic swivel 1200. Teachings of certain embodimentsrecognize that control ports 1114 may also terminate fluid flow in theevent of some system failures. In the example of FIG. 14B, each controlport 1114 is equipped with a solenoid bypass valve. In the event of afull-authority system failure requiring isolation from the conventionalflight control system, for example, IBC system 1000 may remove power tothe solenoid bypass valves associated with each control port 1114. Inresponse, control ports 1114 cut off pressure to their pressurerelief/bypass valves, causing them to redirect system fluid to thehydraulic fluid return lines f that lead back to reservoir 1500.

As will be explained in greater detail below with regard to FIGS. 17Aand 17B, two or more radial fluid devices 900 may operate in parallel.In this scenario, damaging control force fighting between IBC actuatorsmay occur if the displacement control outputs are not correctlysynchronized. Should pressure synchronization fail or a blade actuatorbe inadvertently bottomed on a stationary vane, for example, damagingcontrol pressures and actuator loads can be induced.

Teachings of certain embodiments recognize the ability to provideposition sensors for synchronizing operations between multiple radialfluid devices 900. In some embodiments, position sensors may be providedon positioning pistons 913-915 which are discussed above with regards toFIGS. 13A-13K) and/or the higher-harmonic cams of each radial fluiddevice 900. In these embodiments, however, the position sensors may nothave the appropriate resolution to control force fights in a rigidsystem. Accordingly, teachings of certain embodiments recognize thecapability to monitor control port pressure for each IBC actuator tocontrol force fights between IBC actuators. In one example embodiment,each control port 1114 includes a position sensor 1116. Position sensors1116 may measure the displacement distance of the control valveassociated with each control port 1114. One example of position sensormay include a linear variable differential transformer.

In some embodiments, each control port 1114 may respond to changes incontrol port pressure by displacing its control valve proportionally tothe pressure change. Each position sensor 1116 may measure the amount ofdisplacement of each control valve. If control port pressure exceeds anallowable threshold, valves 1114 may port excess pressure to the returnfluid system. Valves 1114 may isolate the system following a failure byapplying electric power to the solenoids associated with valves 1114 andcausing all control ports 1114 to port fluid to the return fluid system,effectively bypassing the entire system.

FIG. 14C shows hydraulic swivel 1200 according to one exampleembodiment. Hydraulic swivel 1200 includes a rotating portion 1222 and astationary portion 1224. Rotating portion 1222 includes ports 1222a-1222 d that communicates fluid between blade actuators 1300 a-1300 dand non-rotating portion 1224. Rotating portion 1222 also includes port1222 e, which communicates system fluid between blade actuators 1300a-1300 d and non-rotating portion 1224. Rotating portion 1222 includesport 1222 f, which communicates return fluid between blade actuators1300 a-1300 d and non-rotating portion 1224.

Rotating portion also includes rotary seals 1223 between each port 1222a-1222 f. Teachings of certain embodiments recognize that providing bothport 1222 f for return fluid and seals 1223 may extend seal life andreduce or eliminate issues associated with nuisance leakage.

Rotating portion also includes wiring for communicating signals fromblade actuators 1300 a-1300 d to the non-rotating portions of IBC system1000. In one example embodiment, the wiring includes two wires for eachposition sensor associated with the blade actuators 1300 a-1300 d plusthree common wires for each blade actuator providing excitation power.

Stationary portion 1224 includes fluid lines 1224 a-1224 d thatcommunicates fluid between ports 1222 a-1222 d and fluid lines a-d.Stationary portion 1224 also includes fluid line 1224 e, whichcommunicates fluid between port 1222 e and fluid line e. Stationaryportion 1224 includes fluid line 1224 f, which communicates fluidbetween port 1222 f and fluid line f.

FIGS. 15A-15F show blade actuator 1300 a according to one exampleembodiment. FIG. 15A shows a top view of blade actuator 1300 a, and FIG.15B shows a side view of blade actuator 1300 a. Blade actuator 1300 a isoperable to change the position of blade 120 a during operation ofrotorcraft 100. Similarly, blade actuators 1300 b-1300 d are operablechange the positions of blades 120 b-120 d, respectively.

In the example of FIGS. 15A-15F, blade actuator 1300 a is a hydraulicrotary vane actuator. In some embodiments, a hydraulic rotary vaneactuator may be powered at the root of each rotor blade. Teachings ofcertain embodiments recognize that vane actuators may have reducedleakage due to their dependency on a rotary seal, as compared to anequivalent-power linear hydraulic actuator with a sliding seal. Inaddition, a hydraulic vane actuator may also have a higher relativestiffness.

As shown in FIGS. 15A and 15B, blade actuator 1300 a may feature a shaft1302 and a rotary seal 1304 disposed within one or more openings of ahousing 1310. As will be shown in greater detail below, shaft 1302 iscoupled to a vane within housing 1310. In some embodiments, differentshafts 1302 may have different gear splines, and an installer may choosefrom among different shafts 1302 for use with different rotor blades.Rotary seal 1304 is positioned about shaft 1302 and separates theinterior of housing 1310 from the exterior of housing 1310.

In some embodiments, rotary seal 1304 is an elastomeric membrane seal.Teachings of certain embodiments recognize that an elastomeric membraneseal may be suitable in situations where shaft 1302 is limited to acertain range of motion. For example, an elastomeric seal may be coupledto shaft 1302 and may stretch as shaft 1302 rotates so long as shaft1302 does not stretch the elastomeric seal past its elasticity limit. Insome embodiments, angular travel of shaft 1302 may be limited toplus/minus 18 degrees of rotation. In these embodiments, the elastomericmembrane seal may stretch to absorb the plus/minus 18 degrees ofrotation. In addition, as will be explained below with regard to FIG.15D, the elastomeric membrane seal may not be exposed to high pressures(e.g., return fluid pressure of approximately 100 pounds per squareinch), thus limiting the axial hydraulic forces pushing against theseal.

In the example of FIGS. 15A and 15B, housing 1310 includes multiplepieces connected together using bolts 1312. Housing 1310 may alsoinclude connection points 1314 for securing blade actuator 1300 a to therotorcraft.

FIG. 15C shows a cross-section view of blade actuator 1300 a along thecross-section line indicated in FIG. 15B. As seen in FIG. 15C, bladeactuator 1300 a features stationary vanes 1320 and vane impeller 1330.In this example, stationary vanes 1320 define three chambers, althoughother embodiments may define more or fewer chambers. Vane impeller 1330includes three vane surfaces, each vane surface extending into acorresponding chamber between stationary vanes 1320. Vane impeller 1330is coupled to shaft 1302 such that rotation of vane impeller 1330results in rotation of shaft 1302.

Each chamber defined by stationary vanes 1320 includes two openings forcommunicating fluid into and out of the chamber. Within each chamber,the vane surface of vane impeller 1330 separates the two openings suchthat fluid from both openings may accumulate and pressurize on bothsides of the vane surface. In operation, a difference in fluid pressureon opposite sides of a vane surface may cause the vane surface (and thusvane impeller 1330 as a whole) to rotate.

In the example of FIG. 15C, each chamber includes variable-pressurecontrol fluid 1322 on one side of a vane surface. In two chambers,return fluid 1324 is accumulated and ported out of blade actuator 1300.In these two chambers, the pressure of the control fluid 1322 isexpected to be greater than the pressure of the return fluid 1324. Inthe third chamber, approximately-constant system fluid 1326 is providedopposite the variable-pressure control fluid 1324. In this thirdchamber, the system fluid 1326 applies a constant source of hydraulicpressure to oppose pressure from the control fluid 1322 and create ahydraulic spring effect. In this example, the first two chambers, incombination, have twice the effective vane area as the third chamber,doubling the ability of the variable-pressure control fluid 1322 to movevane impeller 1330.

In some circumstances, blade actuator 1300 a may be subject to leakage.For example, leakage across rectangular vane surfaces in a rotary vanemay be higher than in piston actuators in a cylinder. Accordingly,teachings of certain embodiments recognize that leaked fluid should beported returned to the system rather than vented to the atmosphere.Teachings of certain embodiments also recognize the ability to use thisleaked fluid to provide a continuous lubrication to support bearings inblade actuator 1300 a and create low pressure areas behind rotary seals1304.

FIG. 15D shows a cross-section view of blade actuator 1300 a along thecross-section line indicated in FIG. 15A. As shown in FIG. 15D, supportbearings 1340 may support rotation of shaft 1302 within blade actuator1300 a. In this example, leaking fluid may lubricate support bearings1340 and then be ported to the return fluid 1324. In addition, teachingsof certain embodiments recognize that providing return fluid 1324 behindrotary seal 1304 may prevent rotary seal 1304 from being subject to highhydraulic forces.

FIGS. 15E and 15F show cross-section views of blade actuator 1300 aalong the cross-section line indicated in FIG. 15B during operation ofblade actuator 1300 a. In the example of FIG. 15E, hydraulic pressure ofcontrol fluid 1322 is greater than hydraulic pressure of system fluid1326, which forces vane impeller 1330 to rotate counter-clockwise by 18degrees. In the example of FIG. 15E, hydraulic pressure of control fluid1322 is less than hydraulic pressure of system fluid 1326, which forcesvane impeller 1330 to rotate clockwise by 18 degrees.

In some embodiments, multiple blade actuators 1300 may be coupledtogether to operate in series. Teachings of certain embodimentsrecognize that providing multiple blade actuators 1300 per blade mayprovide redundancy and reduce catastrophic failure in the event a bladeactuator fails. For example, FIG. 16A shows two blade actuators 1300 acoupled together in series, and FIG. 16B shows three blade actuators1300 a coupled together in series. In each of these examples, couplingassemblies 1350 couple together shafts 1302 a from different bladeactuators 1300 a.

FIGS. 17A and 17B show redundant IBC systems having multiple bladeactuators 1300 coupled together in series. In FIG. 17A, IBC system 2000features three blade actuators 1300 coupled together in series for eachrotary blade (e.g., rotor blade 120 a is coupled to three bladeactuators 1300 a). IBC system 2000 also features three flight controlcomputers (flight control computers 2100, 2200, and 2300). Each flightcontrol computer is in communication with a corresponding radial fluiddevice 900. Each flight control computer/radial fluid device combinationis operable to control one of the three blade actuators 1300 for eachrotor blade, as shown in FIG. 17A.

In operation, according to one example embodiment, flight controlcomputers 2100, 2200, and 2300 receive cyclic and collectiveinstructions from input device 2050. One example of input device 2050may include a control stick accessible by a pilot. Each flight controlcomputer 2100, 2200, and 2300 programs a radial fluid device 900 toimplement the cyclic and collective instructions. For example, eachflight control computer may send signals indicating how the fundamentalcyclic motion pistons and the higher-harmonic cams of each radial fluiddevice 900 should be positioned.

Each flight control computer 2100, 2200, and 2300 may also receivemeasurements indicating whether blade actuators 1300 are fightingagainst one another. For example, each flight control computer maymeasure shaft rotation speeds, fluid pressures, and/or piston/valvedisplacements. In this example, a difference in these measurementsbetween flight control computers 2100, 2200, and 2300 may indicatingthat two or more blade actuators 1300 may be fighting each other. Thus,flight control computers 2100, 2200, and 2300 may communicate with eachother using cross-channel data links to share synchronizationinformation. As one example, if two blade actuators 1300 aremechanically fighting, the two corresponding flight control computersmay share information indicating that at least one of the flight controlcomputers should adjust fluid line pressure within its portion of theIBC system.

In FIG. 17B, IBC system 3000 features two blade actuators 1300 coupledtogether in series for each rotary blade (e.g., rotor blade 120 a iscoupled to two blade actuators 1300 a). IBC system 3000 also featuresfour flight control computers (flight control computers 3100, 3200,3300, and 3400). Unlike IBC system 2000, two flight control computersare in communication with one corresponding radial fluid device 900. Inthis example, each radial fluid device 900 is in communication withredundant flight control computers, allowing each radial fluid device900 to continue powering blade actuators 1300 even if one flight controlcomputer is disabled.

Teachings of certain embodiments recognize that IBC systems may includeany number of blade actuators, flight control computers, and radialfluid devices. The numbering and configuration may depend, for example,on the safety requirements for a particular rotorcraft.

Modifications, additions, or omissions may be made to the systems andapparatuses described herein without departing from the scope of theinvention. The components of the systems and apparatuses may beintegrated or separated. Moreover, the operations of the systems andapparatuses may be performed by more, fewer, or other components. Themethods may include more, fewer, or other steps. Additionally, steps maybe performed in any suitable order.

Although several embodiments have been illustrated and described indetail, it will be recognized that substitutions and alterations arepossible without departing from the spirit and scope of the presentinvention, as defined by the appended claims.

To aid the Patent Office, and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims to invokeparagraph 6 of 35 U.S.C. §112 as it exists on the date of filing hereofunless the words “means for” or “step for” are explicitly used in theparticular claim.

What is claimed is:
 1. A rotorcraft, comprising: a body; a power traincoupled to the body and comprising a power source and a drive shaftcoupled to the power source; a rotor system coupled to the power train,the rotor system comprising a rotor blade; an actuator coupled to andoperable to move the rotor blade; and a radial fluid device in fluidcommunication with the actuator, the radial fluid device comprising: acylinder block comprising a plurality of radially extending cylindersincluding one cylinder in fluid communication with the actuator, whereinthe cylinder block is mounted for rotation, wherein each radiallyextending cylinder is in fluid communication with a different rotorblade of the rotor system; a plurality of pistons each slidably receivedwithin a different one of the plurality of radially extending cylinders;a cam disposed about the plurality of radially extending cylinders; afirst linear control coupled to the cam and operable to reposition thecam along a first axis; a second linear control coupled to the cam andoperable to reposition the cam along a second axis; and a third linearcontrol coupled to the cam and operable to resist movement of the camalong a third axis.
 2. The rotorcraft of claim 1, wherein at least oneof the first linear control and the second linear control is operable tomove the cam during rotation of the cylinder block.
 3. The rotorcraft ofclaim 1, wherein the cam comprises a circular surface in contact withthe plurality of pistons.
 4. The rotorcraft of claim 1, wherein the camis single-lobed.
 5. The rotorcraft of claim 1, wherein each piston ofthe plurality of pistons completes one stroke per revolution of thecylinder block.
 6. The rotorcraft of claim 1, wherein: the radial fluiddevice further comprises a housing defining a first housing cylinder, asecond housing cylinder, and a third housing cylinder; the first linearcontrol comprises a first control piston slidably received within thefirst housing cylinder; the second linear control comprises a secondcontrol piston slidably received within the second housing cylinder; andthe third linear control comprises a third control piston slidablyreceived within the third housing cylinder.
 7. The rotorcraft of claim6, wherein: the first housing cylinder is operable to receive a firstfluid; the second housing cylinder is operable to receive a secondfluid; and the third housing cylinder is operable to receive a thirdfluid.
 8. The rotorcraft of claim 7, wherein the first and second fluidshave varying pressures and the third fluid has an approximately constantpressure.
 9. The rotorcraft of claim 1, wherein the first linear controlcomprises a first control piston slidably received within a firsthousing cylinder.
 10. The rotorcraft of claim 9, further comprising aposition sensor operable to measure movement of the first controlpiston.
 11. The rotorcraft of claim 10, wherein the position sensor is alinear variable differential transformer.
 12. The rotorcraft of claim 1,wherein the cylinder block further comprises a second plurality ofradially extending cylinders, the radial fluid device furthercomprising: a second plurality of pistons each slidably received withina different one of the second plurality of radially extending cylinders;and a second cam disposed about the second plurality of radiallyextending cylinders, wherein the second cam has at least one more lobethan the cam.
 13. The rotorcraft of claim 12, wherein the cylinder blockfurther comprises a third plurality of radially extending cylinders, theradial fluid device further comprising: a third plurality of pistonseach slidably received within a different one of the third plurality ofradially extending cylinders; and a third cam disposed about the thirdplurality of radially extending cylinders, wherein the third cam has atleast one more lobe than the second cam.
 14. A method of providingcyclic control of a rotor blade, comprising: providing a cylinder blockassembly comprising: a cylinder block comprising a plurality of radiallyextending cylinders including one cylinder in fluid communication withan actuator associated with a rotor blade, wherein the cylinder ismounted for rotation, wherein each radially extending cylinder is influid communication with a different rotor blade of the rotor system; aplurality of pistons each slidably received within a different one ofthe plurality of radially extending cylinders; and a cam disposed aboutthe plurality of radially extending cylinders; applying a first forceagainst the cam along a first axis; applying a second force against thecam along a second axis; and applying a third force against the camalong a third axis, wherein applying the first, second, and third forcesis operable to position the cam relative to the cylinder block.
 15. Themethod of claim 14, further comprising rotating the cylinder block suchthat rotation of the cylinder block causes each of the plurality ofpistons to stroke.
 16. The method of claim 14, wherein applying thefirst, second, and third forces is further operable to position the camrelative to the cylinder block during rotation of the cylinder block.17. The method of claim 14, wherein applying the first force comprisessubjecting a piston coupled to the cam along the first axis to a fluidpressure force.
 18. The method of claim 14, wherein applying the thirdforce comprises subjecting a piston coupled to the cam along the thirdaxis to an approximately constant fluid pressure force.
 19. The methodof claim 14, further comprising rotating the cylinder block such thatrotation of the cylinder block causes each of the plurality of pistonsto stroke.
 20. A radial fluid device, comprising: a cylinder blockcomprising a plurality of radially extending cylinders, wherein thecylinder block is mounted for rotation, wherein each radially extendingcylinder is in fluid communication with a different rotor blade of therotor system; a plurality of pistons each slidably received within adifferent one of the plurality of radially extending cylinders; a camdisposed about the plurality of radially extending cylinders; a firstlinear control coupled to the cam and operable to reposition the camalong a first axis; a second linear control coupled to the cam andoperable to reposition the cam along a second axis; and a third linearcontrol coupled to the cam and operable to resist movement of the camalong a third axis.
 21. The radial fluid device of claim 18, wherein atleast one of the first linear control and the second linear control isoperable to move the cam during rotation of the cylinder block.
 22. Theradial fluid device of claim 18, wherein the cam comprises a circularsurface in contact with the plurality of pistons.
 23. The radial fluiddevice of claim 18, wherein the cam is single-lobed.
 24. The radialfluid device of claim 18, wherein each piston of the plurality ofpistons completes one stroke per revolution of the cylinder block. 25.The radial fluid device of claim 18, wherein the cylinder block furthercomprises a second plurality of radially extending cylinders, the radialfluid device further comprising: a second plurality of pistons eachslidably received within a different one of the second plurality ofradially extending cylinders; and a second cam disposed about the secondplurality of radially extending cylinders, wherein the second cam has atleast one more lobe than the cam.
 26. The radial fluid device of claim18, further comprising a housing defining a first housing cylinder, asecond housing cylinder, and a third housing cylinder, wherein: thefirst linear control comprises a first control piston slidably receivedwithin the first housing cylinder; the second linear control comprises asecond control piston slidably received within the second housingcylinder; and the third linear control comprises a third control pistonslidably received within the third housing cylinder.
 27. The radialfluid device of claim 20, wherein: the first housing cylinder isoperable to receive a first fluid; the second housing cylinder isoperable to receive a second fluid; and the third housing cylinder isoperable to receive a third fluid.
 28. The radial fluid device of claim26, wherein the first and second fluids have varying pressures and thethird fluid has an approximately constant pressure.
 29. The radial fluiddevice of claim 18, wherein the first linear control comprises a firstcontrol piston slidably received within a first housing cylinder. 30.The radial fluid device of claim 28, further comprising a positionsensor operable to measure movement of the first control piston.
 31. Theradial fluid device of claim 29, wherein the position sensor is a linearvariable differential transformer.